Even if you're improvising, the fact that beforehand you know certain things will work helps you make those improvisations successful. It really helps to have a certain amount of knowledge about musical structure.
“I was a starter and did some good things there, and then I got a chance to prove myself as a closer. Because of that opportunity, I was blessed with the honor of being elected to the Hall of Fame.”
“It's so clear cut with a comedian - you have that reflex action, whereby you laugh or you don't. And so you either love us or you simply cannot see why people are laughing.”