My Little Pony: Friendship is Magic, Season 3

Pinkie Pie:
Wait! If I'm not here when Rainbow Dash's letter arrives, I won't be able to read it right away, and if I don't read it right away I won't be able to write her back right away, and if I don't write her back right away, she might think I didn't get her letter and then she might worry about loss and then she's worried about her letter, she'll be distracted and if she's distracted then she won't do well in the Academy and if she doesn't do well in the Academy, then she'll get kicked out and if she gets kicked out she'll never get to be a Wonderbolt and if she never gets to be a Wonderbolt all her dreams will be crushed! And it'll be ALL. MY. FAULT!

Applejack:
So... in other words, you're stickin' by the mailbox.

Pinkie Pie:
Yup.