Eh, that's a hard one, since I don't keep too many of those on hand. I liked the Animaniacs "if at first you don't succeed, blame it on your parents" and likewise Homer's "If something's hard to do, then it's not worth doing!" and Bart's follow-up "Can't win, don't try, got it." But I guess if we're going life philosophy then Cesar Millan's "God doesn't give you the dog you want, he gives you the dog you need" which is probably adapted from "things", which is what I go with, but I'd rather attribute it to him, since he's my spiritual advisor and everything. That is usually how I keep on an even keel is by believing that the universe knows it's doing and I should just go with the flow and it works out.
Although my current favorite is taken from Batman TAS of "If you keep playing chicken...you're gonna get fried." Which we then apply to EVERYTHING for lulz.