My dear Pink Sparkle, if we're going to talk about the Princess of Friendship, we should start with her very first friend...
"Attention class, may I have your attention please?" the teacher spoke to her students, standing in front of the class. "Now, we have a new student in our classroom today, and I want you all to make her feel welcome."
"Wow, a new classmate!" Minuette giggled, looking over to her friend, Lemon Hearts. "You, like, think she's from Canterlot, or from another school somewhere else?"
"Oh, it's probably some new girl from some place like Ponyville." Twinkleshine piped up from behind them. "Ohhh, I'd love to go there and see all the cute animals on the farms!"
"Gee, I hope she's nice!" Lemon Hearts added with a laugh, looking over to the filly with her face buried in a book next to her. "Hey Moondancer, what do you think the new filly will be like?"
"Oh, It's probably that new wonder student I overheard them talking about when I was trotting by the teacher's lounge. The one's who is the princess' personal student." Moondancer snorted dismissively, not even bothering to look up from her book. "I've heard something about her hatching a dragon's egg or something... and I really can't say I'm very impressed."
"Moondancer, I don't think anything impresses you." Minuette laughed, rolling her eyes. "How can you NOT think a being able to hatch a dragon was awesome?!"
"It's probably just some story cooked up to make Princess Celestia's personal student look good." Moondancer shook her head. "She probably got into this school because she's the princess student. I doubt she passed the test, and earned her way in like we did."
As the students whispered to each other, a little purple unicorn filly with a striped mane trotted into the room. "Class, this is Twilight Sparkle, Princess Celestia's personal student. I want you all to be nice to her, and make her feel welcome!"
The little filly quietly trotted over to the nearest empty seat, which just happened to be right next to Moondancer. Twilight waited hesitantly for a few moments before Minuette spoke up.
"Hey, so you're Twilight, huh? Nice to meet you!" The toothpaste-colored filly greeted her excitedly. "I'm Minuette, and these are my friends, Lemon Hearts and Twinkleshine!"
"Oh, hello!" Twilight replied, giving the three other fillies a small smile. "It's really nice to meet all of-"
"Oh wow, so you're Princess Celestia's student!" Lemon Hearts exclaimed. "That's so cool! How did you meet the princess? How much magic has she taught you?"
"Well actually, I just started taking some basic lessons from her highness," Twilight replied. "but I have read some books about-"
"Have you learned any really cool spells?" Twinkleshine squealed. "Maybe you could teach us some magic!"
The three fillies continued to talk with the new girl, as Moondancer buried herself deeper and deeper into her books. When the others finally lost interest and went back to mess around the teacher's desk. Twilight sat there in silence for several minutes, before finally speaking up to the other filly.
"Umm, excuse me..." she asked Moondancer. "but would you mind if I took a look at the other book you've got there?"
Moondancer looked out from behind her book, raising an eyebrow. "Sure, go ahead." The unicorn filly shrugged. "Knock yourself out."
Twilight sat down beside her, and picked up the books. The two fillies were both deep into their reading, when Twilight spoke up again.
"Say, I just started reading about unicorn history, and I'm really fascinated by all the powerful pony wizards and sorceresses there have been." Twilight looked up from her book at the other filly. "I'm especially impressed by the great wizard, Hayscartes."
"Hayscartes? Pshhhh!" Moondancer rolled her eyes, pointing a hoof to a page in her book. "Oh, please! He was barely a second rate magician! Now, Starswirl the Bearded, that was a wizard worth his horn! Nopony could create a spell like he could!"
"Starswirl the bearded?" Twilight asked, looking over Moondancer's shoulder. "Oooo, I've heard about him! Didn't he explore the caverns of Maretonia?"
"Actually, it was called Mirtania then." Moondancer corrected her, levitating another book up for Twilight to look at. "Here, take a look at his biography, it's really incredible!"
The two little fillies hit it off instantly, and began spending all of their free time together. They would be busy studying, practicing simple spells, and working on school projects together. Oh, the two often hung out with Twinkleshine, Minuette, and Lemon Hearts; and the group even made a new friend, Lyra Heartstrings. But while those three were busy having fun and getting their heads stuck in lab beakers, The two other unicorn fillies poured all their time into their studies. The two were so focused on their studies, they didn't notice the influence they were having on each other.
"Hey Twilight, have you ever, like, noticed how much you and Moondancer are alike?" Minuette giggled. "I'm mean, the two of you are practically like twins!"
"WE ARE NOT!" the two replied in unison, both yelling in the same voice and tone. "Why would you even SAY that?!"
"Oh yeah, I can totally see it! Same mane style, same tail style..." Lemon Hearts agreed. "You're like twins, or something!"
As the years passed, the two buried themselves more and more in their studies, to the point their other friends stopped asking them if they wanted to hang out outside of school. By the time the fillies reached their teens, though, the two magic nerds were starting to take interest in other things. When they were both fourteen, they had decided to have a study-sleepover at Twilight's house, when Moondancer came to an interesting revelation....
"Bye, mom! Bye, dad! I'm off to pick up Cadence for the prom!" Shining armor declared, putting on his letter jacket, and trotting out the door. "See ya later, Twily!"
Moondancer watched the older teen stallion go, her eyes focused on his backside a little longer then they probably should have.
"Uhhh, what are you staring at?" Twilight asked in confusion, looking up from the textbooks they had scattered all over the kitchen table. "That's just my brother, leaving for his date."
"Oh, I was just admiring Shining Armor's... superior anatomy," Moondancer replied, adjusting her glasses to hide her reddening face. "You know, for a unicorn, he has muscles as big and tight as an earth pony."
Twilight stared at the other mare in confusion for a moment, before realization dawned on her.
"You think Shining Armor is hot!? EWW!" Twilight stuck her tongue out, in horror and disgust. "He's my brother, that's so totally GROSS!"
"Oh, really?" Moondancer asked, lowering her glasses to stare at her friend. "And what about those muscle stallion calenders you have hidden in your textbook covers, Twilight? Or those musclebound stallion pin-ups you keep hidden in your-"
"OKAY Okay! Keep it down, would you?" Twilight whispered, afraid her parents would overhear. "Let's... let's just get back to our studies, okay?"
The two fillies learned magic together, but as time went on, they became so buried in their studies, that friendship almost seemed to become of secondary importance. Oh, the two were still friends, of course. But as time drifted on, the two fillies began to drift apart.... until the day Princess Celestia sent Twilight away.
"How could she just leave, HOW?!" Moondancer cried out in sadness, after everypony had left her party. "She didn't even say goodbye! What kind of friend is that?!"
And with Twilight leaving her behind, Moondancer was left feeling alone. Twinkleshine and the other fillies tried to cheer their friend up, but she would open herself up to other ponies no longer. And so, the future princess of friendship, had managed to break the heart of her first friend...
"Wait, you mean the Princess of Friendship did that? But... I thought she was a perfect pony, who never made any mistakes!"
"This should show you, my dear Princess Pink Sparkle, that nopony... nobody, as you ponies say today... is really perfect. But now, let us take a look into how this first broken friendship resolved itself..."