Ever since Pinkie Pie joined the resistance against the changelings, she had made it her mission to make everypony there smile. After all, when she was a little filly she never knew what fun really was, and then even as an adult she hadn't-- not until Celestia finished off that meanie Nightmare Moon one day and released this big rainbow. It was so big and impressive and pretty, and it made something inside of Pinkie tingle, like it was familiar and right. Like it should have happened differently. But really it didn't matter when it happened, because it did, and all those colors and the relief that spread after the Nightmare was vanquished showed her just how happy somepony could be!
And when Princess Celestia fell into such a terrible sadness after that, and when Discord made ponies sad before he too was slain, and when the Changelings came back and ruined so many of those happy smiles... Pinkie Pie figured out what she was meant to do. What she was meant to be. It was her duty, her destiny to bring those smiles back some day, one happy face at a time, and she had the Cutie Mark to prove it.
When she joined the resistance, she then had the Changeling-vanquishing weapons to prove it.
Then there were all the members who saw all kinds of bad stuff happening to ponies everyday, which gave her even more of a job to do; she had to get all of those ponies giggling and friend-making!
It was hard.
It was hard, so hard, to get them to see the positive side, to hear even a single chuckle. Everypony was just so serious all the time, for good reason, and sometimes it felt like they didn't really want to be happy. Which was ridiculous! Yeah, there were all kinds of nasty things happening, but that was why they had to keep their heads up high and spread good cheer! But they all just kept on ignoring her, and seemingly not knowing how to smile, just like Pinkie Pie used to be before she saw Princess Celestia get rid of Nightmare Moon. So it was hard. And tiring. And maybe a little soul-crushing.
Especially when it came to Fluttershy.
Pinkie Pie had been trying everyday for months to become Fluttershy's friend, or make her feel even the tiniest bit better, but it ever worked. Fluttershy continued to grumble, to sigh, to cry herself to sleep at night when she thought nopony was listening. To snap at Pinkie Pie, tell her how annoying she was being, say to her, "You can't trust anypony anymore. You never could. When I was a filly all they would do was say awful, t-terrible mean things and mock me for not being able to fly. Now I'm surrounded ponies who could be Changelings in disguise, and ponies like you, who-- wh-who pester everypony with their trivial, dumb passions that nopony gives a flying feather about! Leave me alone!"
Hearing that just made everything worse. Seeing Fluttershy everyday made it all feel so heavy. But she couldn't stop trying. For some reason, ever since she saw Fluttershy for the first time her Pinkie Sense had been going off like crazy, with her Cutie Mark tingling and that aching song in her chest telling her that Fluttershy was special. They were meant to be friends, Pinkie Pie could feel it! Her Sense just kept on dizzying and doozying about it, so of course it was true, and--
Pinkie Pie couldn't give up. Not for anything. Nopony was happy in Equestria. Nopony laughed. Nopony smiled. Laughter was gone, everypony was a little less kind, and it was so sad because Pinkie Pie felt so very deeply in her soul that it could be different. If only everypony tried.
So Pinkie Pie got up every morning, did her patrols, set her traps, and then she went back to her hut and planned: parties, dances, songs, jokes, any little shred of possible happiness she could plan. She talked to Fluttershy every day, let Fluttershy scream at her until her throat was scratchy and Pinkie Pie could feel herself crying, could feel herself almost believing what this awful mean toxic poor hurting mare had to say, but not quite. She saved ponies from monsters, chased away changelings, kept her head up. Pinkie Pie smiled. She laughed. She tried, even when it felt like she was going to break.
And at the end of the day, she didn't end it all. Not when she really wanted to. Not when Fluttershy got mad and told her to.
Pinkie smiled instead.
Because she couldn't let the Laughter die forever, not when something so beautiful was surely on the horizon.