My favorite quote is
"You can't win unless you know how to lose."
-- Kareem Abdul Jabbar
I like this quote because, if you lose you learn from your mistakes and then try to win. if you always win then its no fun to win because you don't know what it's like to lose which is no fun. Also if you lose you can't say the other team cheated just because you lost, and if you win you can't tease the other team.