Woody Allen stayed so good because he never left New York. Howard Stern stayed so good because he never left New York - Mel Brooks when he just got out of New York was doing 'Blazing Saddles;' when he left New York he started doing stuff like 'Robin Hood Men In Tights' - he was in L.A. too long. He lost the edge.
All I can say is that you only realize how big your mountain is once you're laying motionless, helpless, and hopeless in the valley below. No one goes there on purpose, if you get what I'm saying, because the only way to find your personal low is to slip and roll down that mountain of yours, straight through to the bottom, no holds barred.