The fillies learn that needing is one thing, and getting is another. Also, there are Lebowski-ponies!
Season 2, Episode 5: "Sisterhooves Social"
I'm the youngest of four children, and the only girl. My oldest brother was born in 1962, but I didn't hit the scene until 1973, so we didn't grow up together. Also, if you believe the U.S. Census Bureau, he's the one of the last of the Baby Boomers, while I'm about as Generation X as they come. (He doesn't identify as a Boomer, though, and I don't blame him.)
This is roughly the same age dynamic as Rarity and her younger sister Sweetie Belle, the latter of whom has already nearly caused a fire (or possibly opened the Ark of the Covenant) with a misbegotten attempt at breakfast in bed for Rarity.
The next surprise comes in the form of their parents announcing that their week-long vacation begins today, and Sweetie Belle will be staying behind with Rarity
Sweetie Belle is terribly excited ...
... Rarity, not so much, especially since she has a lot of work to do. I've said it before, and I'll say it again: For all her vanity and princessocity, Rarity has a strong work ethic, and a successful career that's she built from the ground up. That's gotta count for something.
As the day goes on, Sweetie Belle's attempts to help her sister and/or not be bored to death fail in increasingly catastrophic ways.
DEFCON 5: Doing laundry without being asked, and shrinking an incredibly expensive one-of-a-kind designer crocheted wool sweater in the process.
DEFCON 4: Drawing -- an activity that's never gotten her into trouble before -- and decorating the drawing with rare gems that Rarity was saving for a client's outfit.
DEFCON 3: Now under orders to clean up the mess she made and not create a new one, taking it a step further and cleaning up Rarity's quote-mess-unquote, too.
DEFCON 2: Asking one of the most perplexing questions of childhood, about the "do as I say, not as I do" double standard of adults: How come Sweetie Belle gets in trouble for being messy, but Rarity gets away with it?
As Rarity sinks further into eye-twitching madness, Sweetie Belle goes elsewhere to lament.
Apple Bloom hears said Sweetie Belle's lamenting and points her toward the fliers littering Ponyville: The Sisterhoof Social at the Apple family farm! (I love text on the show always looks like a cross between Russian and how words look in a dream.)
Rarity is typically dismissive of anything involving dirt, leading to DEFCON 1:The fight in which they both say things they shouldn't.
Sweetie Belle retreats to Sweet Apple Acres, where Applejack (who's had her own conflicts with Rarity) consoles her.
Sweetie Belle also sees what it looks like when sisters work together, and it's pretty enticing.
Rarity, for her part, is having difficulty holding her grudge. (Speaking from experience, maintaining a grudge against a sibling is exhausting work.)
But she realizes that not only has Sweetie Belle's reorganization lead to new inspirations, Sweetie Belle really loves her, and having a sister is perhaps not so bad after all. She even does her best Scarlett O'Hara.
The problem is that Sweetie Belle, understandably enough, has decided that she'd rather have Applejack for a big sister.
Applejack is very much opposed to this, but Sweetie Belle is not won over by Rarity's desperate attempts at reconciliation, most of which involving doing Rarity's favorite things.
Sweetie Belle harumphs off, and Rarity misdirects her anger as usual.
But Applejack has a plan.
The next day at the Social, Applejack and Apple Bloom announce that Applejack is now Sweetie Belle's sister for one day -- but only one day, as Apple Bloom frequently reminds her -- so they can run the race together.
The green-eyed Applejack promptly falls into a mud hole and emerges with blue eyes, not that Sweetie Belle notices. Enh, I'm no good with eye color, either.
They lose the race. Sometimes, even with teamwork, you're going to lose.
But that's okay, because they did it together, and ... Applejack's hat falls off to reveal a horn -- it was Rarity all along! At least, since the mud hole.
In the joint Shoehorn, Rarity and Sweetie Belle relate that being a sister is great but hard work, filled with compromise and dirty-ish hooves.
I am sans sister, but I think that holds true for having brothers, too.