Quote by David Letterman
"If you have to think about whether you're happy, you're not."
More from David Letterman
"I think it's nice when people use your name when they're greeting you. It makes you feel like more than just a guy."
"The difference between me and my competition is that I'm awake."
"You know, it's hard to beat a person at anything unless they want to lose."
"If you want to know what God thinks of money, just look at the people he gave it to."