This is from "What Makes People Laugh," an interview by Carl Arnheiter with Jon Stewart. It appears in the book Rejected: Tales of the Failed, Dumped and Canceled, by Jon Friedman.
What's your take on building a joke, how does it start for you?
Jon Stewart: It's 99% perspiration and 1% love and all that...I think it's just one of those things you learn from doing it, and you know, the funny thing is even though I know how to do it in that yeoman sort of way, there is no "oh now I got it and so it now pours out." But it still takes as much effort and all that, I can do it a little quicker than I used to be able to, but the great stuff still comes in the same percentage that it ever came.