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Tear Jerker: Life In Manehattan
Honey Do explaining why she hides her identity: too many ponies assume that the way Daring Do acts in the books is who she really is. The fictional Daring is a brash, Hot-Blooded, prideful character, while Honey Do's a Humble Hero. Yet even her old friends started mistaking the grossly exaggerated and changed character for 'the real her'.
Orange Sherbert's slow estrangement from the rest of the Apple Clan, and her belief that they all see her as a Gold Digger who only married Mosely for money.
Part of what cemented this was when one of her cousins filed for bankruptcy. She sent him a check, only for him to mail it back with a note:
Keep your check, that's Orange money.
This culiminated with what she saw as Her Greatest Failure: her inability to bond with Applejack when the filly came to visit. AJ declared she wanted to be a socialite 'just like her', but grew disallusioned with the lifestyle. Despite all of Sherbert's efforts to bond, she found AJ leaving a week later, saying only "I'm going back to my farm. I'm going home."
The Reveal of just WHY Applejack is so determined to make the latest Apple Family Reunion so memorable: Without Twilight around to mitigate her stubborn pride, she didn't seek help during Applebuck Season until it was too late. Half the crop spoiled, and another third was lost because she was too exhausted. She had to take out a second mortage on Sweet Apple Acres, and Capital Gain was going to forclose on the farm just three days after the reunion. This all comes out when he shows up to claim it early.
Applejack admitting to Twilight that the reason she didn't seek out help from her Uncle and Aunt Orange was fear that they'd run Sweet Apple Acres far better than she ever could.
"Mama, are you a bully?"
Trixie's Backstory, as revealed in Brag You Down. She was the first member of the Lulamoon family to fail the entrance exam for Canterlot's School for Gifted Unicorns, and had to watch as all her childhood friends moved on without her. Her mother, disappointed by her failure, became distant and neglectful. Convincing herself that her talent was meant to be shared with the world, she ran away from home, and probably would've had to return with her tail between her legs if she hadn't met Hairy Hoofdini. The Amazing Hoofdini took her in as an apprentice, and they traveled together for five years... until his tragic death.
To expand upon the above: A scam artist proposed he take the Steel Soul challenge, in which the performer took a cannonball to the chest. Though Hoofdini correctly explained the simple substitution trick used to pull off the stunt, the charlatan paid a teleportation expert to ensure a REAL cannonball struck him. The con artist was cheered for 'defeating Hoofdini', while Hoofdini was booed while being carried away. Though the ponies responsible were later punished severely, that didn't change the tragedy that'd taken place.
What's worse is Trixie was the only one to attend his funeral.
This has been retconned so that Hoofdini only ended up in a coma, which arguably makes it worse, since Trixie is the only one who hasn't written him off as good as dead.
Trixie forced to go back home with her mother and the effect it has on all the others with her no longer around.