In Defense of the Mary-Sue (And Gary, Too) · 3:26pm Jun 23rd, 2018
I have no patience left for critical discussion that takes the term "Mary-Sue" seriously.
Look, I get it. Back in the day with fanfiction emerging as a popular new form of fan-art, maybe this was a useful concept. I suppose there's still circles of new and developing writers who can be introduced to it as a simplified version of more complex writing ideas. It's not completely without merit, I guess. But I admit these things only begrudgingly, because the more the term comes up the less I want to engage with it seriously.
Look, I can't force you to write or read in any particular way. That is beyond my power. But what I can do is just beg you, all of you reading this, to give those stupid wish-fulfillment characters a chance. Also I am going to take an entire blog post to explain why you should consider giving a pass to that stupid red-and-black alicorn OC vampire hunter demon crime guy character who popped up in your feed.
Seriously.
So I feel like this discussion really needs to start with establishing what a Gary-Stu even is. Or a Mary-Sue. Or - god there's so many variants, I can't even, argh. Look for the rest of the post please assume I'm using the terms basically interchangeably, because the differences are mostly cosmetic.
So in a popular, colloquial sense, the Mary-Sue is often identified with two kinds of characters that have some level of overlap. First, there are 'paragon' characters who have a level of hypercompetence and good fortune that exceeds every narrative challenge put in front of them. Then there are idealized self-inserts of the sort normally found in fanfiction. Your Mary-Sue could be one or the other, and sometimes they are both. The point is that the very idea of a Mary-Sue just sends some people up in arms. There are serious debates about whether canon characters from various popular shows count as Mary-Sues or not. (See: Wesley Crusher, Star Trek TNG)
So my problem with this is so disorganized and broken into tangents that I feel like I have to just stream of consciousness all my objections and stray thoughts and then recategorize them into broad chunks and I'm sorry but that's what you get, you signed the contract.
1. Question - Why is the Mary-Sue Bad?
Now this seems like it should be a really obvious question, right? Of course Mary-Sues are bad, otherwise there wouldn't be so many people joking about them or complaining about them on the internet! Right?
Honestly, I feel like this is a step most people ignore or skim over when explaining the problem with the Mary-Sue as a concept. Since I'm about to collectively dunk on the opinions of a lot of otherwise very intelligent people, I'm going to try my absolute best not to strawman what I think the strongest (or at least, most common) explanations for "why the Mary-Sue is bad" are before I eviscerate them. If I've failed, well, there's a comments section for a reason.
1a.) What's the Problem with Hyper-Competence?
So the two most commonly cited reasons Mary-Sues are bad conveniently correspond to each of the two overlapping archetypes that get called a Mary-Sue. The first has to deal with that paragon/hypercompetent character idea I mentioned earlier. In this reading, the problem with a hypercompetent central character like a Mary-Sue is that hypercompetent characters cannot be adequately challenged by the external threats the narrative puts in front of them. It's a violation of the rule that says stories need tension to function correctly. If the main character can't be threatened or challenged, you lose that tension.
To a degree, this is a pretty salient point. The classic three-act storytelling structure is Man Gets up a Tree, Throw Rocks at Him, Man Gets Down Safely. Two of the three parts of that arc - the man getting up the tree and throwing rocks at him - don't work nearly as well if the man in question is Clark Kent and rocks just bounce off his perfect abs. If the character is, by virtue of their birth, immune to the dangers posed by rocks, it's probably a bad idea to build rising action out of hurling rocks at those characters.
Now I'm sure some of you reading have caught that while there is a problem created if you try to build tension by hurling rocks at Clark Kent, you could fix that problem just as easily by substituting the rocks with kryptonite as you could changing Clark Kent for a different lead. The problem isn't necessarily Clark, it's just as much the challenge the author chose to build rising action with.
In other words, hypercompetence on its own doesn't lead to a worse story. What leads to bad storytelling is a story that tries to build tension out of situations where we know the main character isn't in any real danger or faces no real challenge. Plenty of stories in pop culture have found ways to take incredibly competent heroes and still build fun, tense boilerplate plots around them.
One of the most obvious examples that comes to mind from recent years is of course internet sensation One Punch Man, which uses the hyper-competence of the main character to create conflict. Saitama's ability to win fights in a single blow means that we're never really worried about whether he's in danger - we already know the outcome of a fight before it begins. Instead, the series doubles down on Saitama's internal conflicts to create tension. He's so strong that winning fights no longer brings him a feeling of satisfaction, and it's resulted in him getting less recognition than weaker heroes. When the series does want to do a serious knock-down battle, it shifts focus over to the less-competent supporting cast and builds the tension of the threat by using them as a benchmark, then introduces Saitama as a way to break the tension.
This is hardly a narrative technique only used in parody anime though. Look at old golden age mysteries, particularly the early Holmes stories, Edgar Allen Poe's Auguste Dupin stories, and Agatha Christie's Poirot and Marple stories. The central detective of a golden age mystery story is never in danger of making a mistake - they are so hyper-competent that they seem to have a sixth sense for the significance of details. The tension of a golden-age mystery story isn't in watching the detective solve the crime, it happens directly to the reader as they try to solve the crime before the central character.
In summary, then, hyper-competence of a central character is hardly the source of a story's problems. It's the simple explanation you give to new writers who need to understand that building tension is important and that making your character good at stuff isn't a replacement for forming a connection to the audience. The real, more accurate source of problems is that a story has to build its tension around the limitations placed on it by the central protagonist. An experienced writer needs to learn to both identify what those limitations are, and what that means for the broader story.
1b. What's the Problem with an Idealized Self-Insert?
I'm using the term "idealized self-insert" over "self-insert" here because it's very possible to write yourself into a story without (much) idealizing. Obvious examples here include Ariadne Oliver, Agatha Christie's gigantic self-own of a side character who embodies all of her own quirks and self-criticisms. Most people who have a problem with Mary-Sues as a concept would not have similar objections to Oliver.
Idealized self-inserts, by contrast, are rarely self-owns (at least, intentionally) and even more rarely reflect the reality of the writer. They're not accurate, realistic portraits of an individual, they're fantasies someone has about themselves put to the page. The idealized self-insert isn't always hyper-competent, but they usually display elements of hyper-competence. They tend to become a vehicle for the author's desires, particularly in fanfic - hooking up with the author's bae, hating on characters the author has judged trash, and generally enacting an author's will on an established setting.
Now what I'm going to argue here is that the first and second elements I've just described are best treated as separate problems. The fact that idealized self-inserts are vehicles for authorial fantasy doesn't directly connect to the problem of idealized self-inserts as vehicles for authorial bias.
Let's consider the following. If the Harry Potter books had been written not by a middle-aged British woman but instead by a fifteen year old child with a peculiar scar, would that fundamentally change how you respond to the text?
You might read some elements differently. The fact that Harry is rescued from an abusive household and whisked away to a magical adventure land where he's cast as the hero in a dramatic good vs. evil struggle reads as wish fulfillment moreso than it already does, for instance. You might consider certain characters differently if you knew they were written by a fifteen year old kid. But fundamentally, all of these readings existed in the text already. Whether Rowling is creating a fantasy vehicle for herself or for another person doesn't change the core, underlying fantasy potential of Harry Potter. Those fantasy elements are there regardless of whether the author is directly partaking in them or not.
This is part of why I'm also slowly moving away from trying to critique texts based on whether or not an author is describing their own experiences in them, since ultimately it doesn't matter. One of my least-favorite stories about trans-ness was written by a transgender author, and the fact that they're trans doesn't change any of the underlying problems I had with the story. And that works in reverse, too. If I found out that the guy who draws Food Wars wanted to be a cool dude who is loved by all the ladies in high school - such a stretch, I know - the fact that Soma serves as a fantasy vehicle for that guy specifically wouldn't ruin the story.
On the flip side, let's look at authors inserting their own opinions and biases into stories separately from the idealized self-insert. You don't need an idealized self-insert to clumsily insert your own views into a story. Aside from broad strokes every-work-of-fiction-betrays-the-author's-core-beliefs-in-some-way stuff, there's also concrete examples of preachy works. See: literally the entire bibliography of Ayn Rand, which is explicitly built around her core beliefs regarding individualism, private industry, and the government. There's no one character in the canon of Rand who is literally a stand-in for Rand herself, but reading her work involves getting a double-barrel blast of her politics in the clumsiest way possible.
What makes the idealized self-insert Sue such a bugbear, I think, is that people associate it with characters who embody the worst traits of each approach. Nobody likes it when stories become unbearably preachy without earning the right to it, and nobody likes it when characters feel so much like fantasy vehicles rather than people that they spoil immersion in a story. When characters who are fantasy vehicles also become the vehicle for an author's hot take, the result is that the immersion-spoiling effect compounds and alienates readers.
This is in some ways uniquely true in fanfiction, which is why the Mary-Sue may have actually been a useful concept at one point. In fanfiction, the readers are familiar with a status quo and central cast before a story actually begins. They're invested fairly heavily in elements of this status quo, and have probably already formed their own thoughts and opinions on various elements. This is one of the core advantages fanfiction has over other literary forms - you can expect the audience to have familiarity and investment with your subject matter from the start.
When an author clumsily appropriates bits of this thing the reader is invested in as a vehicle for their own wish-fulfillment and a platform to share their various hot takes on episodes, the experience doesn't just break immersion. It also feels a bit like a betrayal. You were promised My Little Pony, you got something else instead. This poor use of the source material doesn't necessarily mean that the story is bad on its own merits, but the correlation is pretty damn high.
2. So What?
Now if you've made it this far, the big question is what my larger point is. "Mary-Sues are not as bad as they seem" is hardly a hot take after all, at least for me. My larger point is that focusing on Sues as if Sue-ish-ness is the cause of a problem and not a symptom of something else wrong with the story is like putting emphasis on the wrong syllable, or prescribing medicine that treats the symptoms of a disease without identifying a cure. It's the kind of advice that while it's useful in the short term can lead to worse development as a reader and writer in the long term.
For example, what is the point of arguing about whether Character X is a Mary-Sue? I've heard arguments about that very topic in every fandom regarding basically every main character. Katniss Everdeen from The Hunger Games got this treatment. So did Geralt, from the Witcher books. So has Batman, so has Indiana Jones, the list goes on. And the pattern I've noticed with all of these debates is they tend to focus on superficial elements of the character's competence and relation to larger conflicts rather than focusing on how well the story uses them to advance or create conflict. That's actually back-asswards.
On the flip side of this, you have arguments over whether Bella Swan is a Mary-Sue because she's an idealized blank slate character readers can use as a fantasy vehicle. After years and years of hating on Twilight, hating Twilight in a more nuanced way, and then slowly realizing I actually don't really give a shit about Twilight anymore, my response to that debate is that it's stupid and pointless. Bella being a vehicle for reader fantasy doesn't actually change her role in the story, it simply ascribes motivation that may or may not be present as to why certain plot points exist. It's engaging with the text by way of dissing the author as opposed to interrogating the themes or the actual construction.
This kind of criticism where we categorize characters into "acceptable, realistic characters" and "unacceptable Mary-Sue Trash" is such a bad binary for evaluating protagonists that I think once you're out of high school, the most important thing you can learn as a reader and as a writer is to just let it go. You can still use the words, but looking at the Mary-Sue as this binary of good character/bad character is a stunted form of critical readership, and it leads to worse experiences with a text and worse overall critique.
So, yeah. Next time you see the Mary-Sue debate raging around you, please feel free to do what I do: roll your eyes and get back to reading. You'll have more fun this way. Trust me.
I find myself agreeing with about 98% of what you've said here, as I mentioned to you over Discord. I don't really know if there's a precise thing I can identify as where the 2% of disagreement comes from.
If I had to try, I would circle back to your point on how, in past stories (and somewhat in newer age fiction) like Agatha Christie and Edgar Allen Poe, the characters' hyper-competence on whatever their thing was helped to create tension. The same can also be said about characters like Sherlock and Moriarty in Sir Doyle's works. These characters demonstrate a frankly ridiculous aptitude for their skills, but also give us tension in either their failings to properly interact with us normal folk when they try and, when they come up against someone equally hyper competent as in the case of Sherlock v Moriarty, we finally get to "well shit, who is better?" tension.
I ... try not to put too much stock in the Mary Sue argument in terms of reading fanfiction, or any sort of fiction, as I do how the writer uses the characters, the scenarios, and builds tension throughout the piece to judge the product.
Otherwise, well, we get into "Starlight is a Mary Sue" "Oh, really? Let's look at how stupidly competent Sunset Shimmer is" "RABBLE!" "RABBLE RABBLE!" and general faffery.
That is probably about as close as I'll come to nailing down where I disagree with this blog, and yet it's not even a full "absolutely disagree." It's honestly more of a "yes, but" sort of deal.
If I may comment, I think you missed out on a type of Mary Sue as "instantly loved by everybody and always right, and everyone who hates her is a stupid meanie who is just jealous" character. That does overlap a bit with the wish-fullfillment self-insert fantasy but isn't quite that, I think.
The type of Mary Sue that robs the story of any sort of character arc (since the character is perfect to begin with) and any sort of internal conflict.
A greater point I'd like to make as well is that Mary Sues are "bad" because making a character a Mary Sue takes something away from the story: the hypercompetent-sue takes away any tension of external conflicts, the always-morally-right-and-universally-beloved-sue takes away the internal conflict and morality discussion/ambiguity, the wish-fulfillment-sue... Not sure actually. Immersiveness?
And sure, a good author can make a story good despite lesser number of elements, or in fact make a story better for it. But most of the authors that write Mary Sues aren't that good to begin with.
4888108 I would argue that's more a failing of the author than the notion of a hyper competent character, tbh. Using Batman as an example, sure, some comic writers have taken his skills way over the top, but to argue that he is absolutely not good because his hyper competence doesn't allow for any sort of tension ignores a lot of great works.
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I think competence has to be measured relative to the challenges. Sure, Batman is absurdly skilled by any measure when compatlred to any real person, but on his boring day he gets to fight twenty mobsters armed to the teeth, and beat them with his bare hands, or fight a whole gaggle of ninjas, and on his "fun" days he beats up real gods and makes them cry. So he is competent, but not hypercompetent compared to the challenges he faces.
And conversely, Wesley can be all-that on board of Starship Enterprise, but he's hardly "hypercompetent" if the plot demands him to go twenty rounds with the Joker.
So when someone says that character is too powerful, they usually mean it "in comparison to the challenges posed by the plot."
Same goes for cases when characters powers are not even applicable to their challenge -- e.g. Doctor Manhattan who is, for all intents and purposes, a physical god, is not hypercompetent when his challenge is overcoming his passiveness born out of understanding predestination, because it does not apply.
Hmm. Very well put. Focusing on the symptom rather than the disease definitely seems like an apt description of the problems with focusing too heavily on the presence or absence of perceived Mary Sues rather than any other issues a narrative might have. Thanks for a very thought-provoking read.
4888114 All sound points. Very well-put.
I feel like the world of online literary criticism has gone through the same kind of evolution that the MMA world did over the nineties and noughties, and that the concept of a Mary Sue is analogous to the early nineties "Sit & Submit" style of grappling: it is something that was used to confront a problem with some measure of success, but as the environment around it evolved, the useful parts were siphoned off into more comprehensive attacks and it's only effective on targets that never had much going for them in the first place.
"There's no one character in the canon of Rand who is literally a stand-in for Rand herself, but reading her work involves getting a double-barrel blast of her politics in the clumsiest way possible."
Ah, I remember the one time I read Atlas Shrugged. Specifically, most of Atlas Shrugged; I skipped one part after wondering just how long one character's speech on Objectivism was going to go on for and flipping ahead to find it actually had a page count in the double digits.
Thanks for the discussion!
Blast from the past, I think this was the subject of the first blog post of yours that I read.
My opinions haven't changed. Mary Sue is an adjective, not a noun, and it describes a character who is wrecking shit in a story, often in the ways you described.
I'm glad you went into the difference in the ways of being Mary Sue, because from there it's obvious (to me, at least) that there are two different problems that require two different kinds of advice (or warning) to fix them.
If your character is Hypercompetence-Sue, you need, as you pointed out, a challenge worthy of the character (or a character less worthy of the challenge, or some other kind of tension. Either way.)
If your character is Idealized Self-Insert Sue... you just need an audience. The truth about both blank slates and political mouthpieces is that they tend to be hated by everyone except people who identify with their wishes and opinions, who love the hell out of them. And there's nothing wrong with that. It just falls into my standard disclaimer that no one is obligated to like your story, or to not tell you how much they hate it, and if you publish something the public gets to have an opinion on it. All the author needs to do there is find out which half of the cast his readers want in their harem (coughXenophiliacough) or which subgroup wants a dozen page screed expressing their opinions to a gathering of strawmen to have a loved and successful story.
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I think you brought up the same kind of point I had in my On Writing blog that visited the Mary Sue thing. People love Mary Sue when they relate to her, or when the author manages to make you feel like you care about her. A character you love absolutely kicking ass, getting all the mares, etc? Sure! Sign me up! It's just that authors fail at that part so often. They love their Mary Sue already, because she's their baby, and they don't realize that J. Random Reader is not going to feel that love just because.
Maybe it is just because the definitions of Mary Sue I read that were not all that good, but I always understood a Mary-Sue (or Gary Stu) to be a character that is "helped" by the narrative. It is not about being competent or not, being challenged or not, it is about the universe bending around the character to make it easier for him/her without it being remarked upon by the cast.
Things that should be though are being solved by pure luck, characters that don't react the way they are expected to or even "laws" of the story universe being changed, that sort of things.
And even then, I am not saying it cannot be exploited to make something fun or interesting, but a Mary Sue to me described a story in wich a character (usually one that is central to the plot) is given shortcut by the author without any narrative meaning behind it, it is just shortcuts.
Bottom line: I understood a Mary Sue as being the name for the bad narrative, rather then merely the character who is symptomatic of that bad narrative.
There's another dimension of Suishness that I, personally, find the most objectionable. It's a subtype of the gravest of authorial sins where I look upon said worthy in my head spinning their tale as best they can and go "Sorry, pal, I ain't buying it." I can believe that a character is a genius polymath with mad combat skills. Hell, history provides people who are hardly any less remarkable. But a character who knows so much and can _do_ so much must have an explanation. Twilight Sparkle is a magic genius. Even before princessification she was without peer when it came to spellcraft in the show. But you buy it (or I do, at any rate) because she demonstrated precisely the overachieving neurosis you'd expect from someone taught magic by the God-Empress of Ponykind. The character hangs together. Even if not challenged adequately by the plot, Twilight's enough of an enemy to herself (an experience a lot of us will find, I am sure, familiar) that even if the story-universe isn't opposing her there's still conflict.
The reason Rey from the new Star Wars movies gets called out as a Mary Sue so often is that she's not following her archetype. Star Wars is almost _comically_ archetype-based. It's commedia dell'arte with lightsabers, I swear it is. And Han Solo can be a great shot with a blaster and an expert pilot and a few other things besides (I hear he's a dab hand at sabacc) because he's the Well-Traveled Scoundrel. How did he learn all of these things? Why, he's been to $EXOTIC PLACE and learned how to pilot at $UNLIKELY EVENT by $WEIRD STUFF! Of course it is nonsense, because you end up with a character who hasn't lived long enough for all of that to happen to them, but the actual age of the performer isn't important. Han Solo is coded as old and that's just how that one goes.
Rey isn't a Well-Traveled Scoundrel, she's a Callow Youth like Luke before her. And her sworn duty is to _suck_ at things so that she may improve with time. That's how Star Wars operates. She's coded as a character with barely a past, hell, the movie basically opens with her sitting alone wearing a Rebellion helmet, clearly showing us that the character is a dreamer waiting for her adventure to start.
But when action starts she has all these skills and abilities she had nowhere to learn. She isn't coded as a character with vast experience or the sort of grueling childhood training that produces these sorts of skills. Don't get me wrong, Luke was a pretty excellent pilot, but the story explains why. You could have sold the world a techy Rey, the past master of the kludge and the bodge and whatever the Star Wars equivalent of duct tape is. But that's all her backstory and her characterization (especially in Star Wars which relies on archetypes, as I said, to deal with that) will support.
(This, incidentally, is such a strong effect that I walked out of episode seven convinced that she's an amnesiac dark Jedi and that they are going to pull a Revan on us. )
This, incidentally, is why Jyn Erso didn't get called a Mary Sue or, 'lestways, not anywhere I could see. She was pretty damn capable but, crucially, the movie gave her the same checkered past-thing that Han Solo has, and the question of where she got her various skills is easily answered. It's been a rough life and she's been absolutely everywhere.
Amusingly for people obsessed with a 'balanced for competitive play' interpretation of the Mary sue, you can power up the Callow Youth to _ridiculous_ extremes. Indeed, it's a positively magikarpian sort of situation as the Callow Youth must start weak but as growing stronger is sort of what they do, you can have Vin from the Mistborn series who starts the story as the weakest character but _keeps gaining power_ until she's a force of nature.
I feel like 90% of the time, the Mary Sue criticism is a problem with the plot, but the reviewers treat it like it’s a problem with a character. One of the big arguments for Starlight Glimmer being a Mary Sue is that she’s too easily forgiven for her mistakes—but really, how is that Starlight’s fault? The problem (if you do agree that everypony forgave Starlight too easily) is everyone else acting out-of-character to make certain plot beats happen. Or look at how quickly Rey learned to use the Jedi Mind Trick in The Force Awakens. Is it her fault for being too competent with the Force—or the rest of the movie’s fault for not explicitly spelling out where Mind Tricks fall on the Jedi skill tree, and for not reassuring us that it’s reasonable for Rey to already have enough Force Points to unlock that skill?
Obviously, you get into some chicken-and-egg conundrums: how much do the characters move the plot forward, and how much are the characters defined by the plot? And I’m sure there are some cases where the alleged Mary Sue really is the only thing wrong with the story. Still, if the real problem with your story is other characters acting out-of-character whenever your Mary Sue is around, or that the rules of magic in your story are poorly explained and inconsistently applied, I’m not helping the author if all I tell them is “Make that character less of a Mary Sue, and make them less powerful.”
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In short, a Mary Sue is really a wish-fulfillment character who’s failed to find an audience. Batman and Sherlock Holmes are hypercompetent, but there’s no shortage of readers who want to project themselves into those characters, even in badly written stories, so they get a pass. But hardly anyone wants to read about my red-and-black alicorn OC who bears the seventh Element of Harmony and fights with a lightsaber (and the few who would enjoy it are probably too busy writing their own alicorn OC stories), so he’s a Gary Stu.
And that’s why different people can start with exactly the same objective facts about a character—such as Starlight Glimmer or Rey—but disagree on whether they’re a Mary Sue or not. And why the ensuing arguments are always so tedious: because both sides are trying to make objective arguments to prove their own subjective opinions.
If I signed the contract, where is my wish?!
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The whole bit where she absorbed Preservation didn't hurt any, that's for sure.
Then again Sanders is really good at taking Callow Youth and showing how they become badass, with both Vin and Kaladin being good examples of such.
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And that's why he's such a competent writer! Because there's not a thing wrong with a nice power fantasy, but there's a world of difference between being powerful because you grew and being powerful because the world hands you your victories because the writer's on your side. The first is a story that rings true to us: we can all remember being less than we are now. The second just seems like cheating the moment we come to realize the world does not revolve around us.
It may be why adolescents tend to like Sueful characters a bit more. They haven't yet internalized this important truth.
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Actually, in my experience the characters who most resonate with adolescents are in two categories: the characters who start the story already incredibly on top of things, but also the characters who grow over time but grow exponentially quickly. My ur-example for that would be Eragon, who has an entire training arc ripped straight from A New Hope except that he can swordfight and use magic super well by halfway through book one. Later in the books he levels up to the point of being physically equivalent to an elf, who are canonically hypergifted at the Magics.
It's notable that in the case of Eragon, the arc is all there, sometimes in exhausting detail. It only becomes ridiculous if you're reading close enough to realize what a short span of time has actually occurred within the world of the book.
This is one of the reasons I've really gotten over the Callow Youth as an archetype (and probably why Rey bothers me less conceptually, but then I didn't get a chance to see The Force Awakens before I was struck full in the face by d i s c o u r s e ). I don't really have a problem with starting a character at a high or moderately high level of competency, particularly if you do it for the sake of narrative utility. It avoids the need for writing an arc around growing in power/competence and instead lets you focus on the setpieces of the story that are actually fun to read.
Mind you, that's not one-size-fits-all. Getting back to my thesis that it's the tension that makes the 'sue' effect as much or moreso than the character, making a choice about "we're going to make this character more competent than words" means also deliberately making the choice to build the story so that competence doesn't null out narrative threat or spoil the tension you should ideally have in the second and third act.
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Oh, I agree. I'm personally bored senseless by origin stories. I have no problem with characters already starting the story as competent. The problem Rey has is that the movie signals that she's a Callow Youth and then betrays those signals a moment later and then signals again and the resulting semiotic confusion just breaks the movie. In a sense, it's a great illustration of why the new SW movies fail: episode VII in particular is a slavishly copied template but copied without understanding so any changes to the rote formula break it entirely. The good guys are the Resistance, except they live in Republic space so who are they resisting against? Rey's an abused orphan living in the ass end of nowhere except, no, she has a welter of very expensive skills.
And they could have fixed these things trivially. I don't mean rewrite the movie to my nerdish specs. Just a few lines here and there would have fixed at least these two things: explain how the Republic abandoned the less-desirable half of the galaxy to anarchy and the Imperial remnant forces which eventually fell under the banner of the nearest warlord who could offer stability. Have Leia be resisting that and it makes sense and hardly changes a thing. And have Rey give some indication of having somewhere to gain skills. Either give her a complex past, or if you are married to the 'Lone Orphan' motif because you can't not copy episode IV, just give her monastic, meditative aspect. Maybe she scavanged a book of Jedi teachings from somewhere. Maybe she belongs to a religious tradition that's suspiciously Jedi-y that's her one link to her Mysterious Past. Give her something and you could buy it.
But they didn't do any of this because I can only assume the movie was workshopped so much by so many committees that any attempts to fix this got lost in the general buzz of people being stupid.
...so if I can come at this from the other end, this all kind of sparked something that went percolating for a while and finally crystallized. Mary-Sues aren't stupid wish-fulfillment characters in a vacuum. They're stupid wish-fulfillment characters that ruin your enjoyment of other stupid wish-fulfillment characters, including, but not limited to, earlier appearances of the Mary-Sue themselves.
So, like, let's say you were writing a story about someone talking to a space worm about friendship, and you passed on Twilight, Fluttershy, and Moonicorn to put the duties in the hands of some wandering weirdo, who gets fawned over by all and sundry for what a good talk about friendship it was. To the extent that your readers enjoyed rooting for Twilight, Luna, and/or Fluttershy to do things related to space worms, they'll be disappointed that they weren't involved, and are ceding potential achievement in the space worm field to someone else.
"Mary-Sue" is just how that's come to vent, and in a sense it's really perverse, because pretending there's some necessary fictional sin a Mary-Sue is committing extends cover to those situations where what you're ruining is someone's enjoyment of the stupid wish-fulfillment characters that only exist in their head but would totes be doing this so much better OMG.
Part of the reason its so hard to pin down what a Mary Sue is, is that Mary Sues are the result of a confluence of multiple different problems that converge into a single person. To use your own example of the 15-year-old writing Harry Potter and whether or not it is a self insert, it's easy to see what I mean.
Suppose that this 15 year old wrote exactly like JK Rowling. Then, I would think, there's very little reason to think that Harry Potter is suddenly bordering on 'self insert'/mary sueism. While many of the pieces might otherwise be there ("secretly special, rich, tragic backstory, destined to be a hero, etc"), the strength of Rowling's writing, of authorship, prevents those things from making Harry into a Mary Sue. In fact, I would go so far as to suggest that in many cases, accusations of 'Mary Sueism' is the result of the story in question just being poorly written in one way or another.
As good as this post is, tbh 4888145's blog post on Sues, which was lost to posterity when FIMFic did the nsfw blog purge, singlehandedly upended my thinking on them in basically the same way five years ago. After that formulation of "the problem isn't character competence, but a disconnect between what we're shown and told about them" I haven't ever been able to see the poor-writing problem as the fantasy-self problem people generally attack.
I'm glad you're keeping the tradition going of correcting people on that.