One-Line Wisdom

Via a comment left on my last post by Something Different, I discovered a cute blog called BOSD One Liners (what does BOSD stand for?)
It's a compilation of one-liners, some funny, some insightful, some that you've already heard, and some that you haven't.
I like this one, which was posted today:
"People will walk in and out of your life unless you grab their hand and ask them to stay."
Take a look at the site. Which is your favorite one-liner?