Robin Williams and Why Funny People Kill Themselves

This article from Cracked.com is spot-on. (Warning: There is some profanity.)

"Oh, you can’t help that," said the Cat: "we’re all mad here. I’m mad. You’re mad."
"How do you know I’m mad?" said Alice.
"You must be," said the Cat, "or you wouldn’t have come here.”

- Lewis Carroll, Alice in Wonderland