To be a successful standup, you have to have a unique voice. I don't mean the audio quality of the sounds that come out of your mouth, but your own take on the world that's unlike anyone else's. You should have an act that wouldn't sound right if it were done by someone else.
That's what has made the observational comedians of the last two generations so different from those that preceded them. Until the early 1960s, most standups didn't write their own material. They hired joke writers, and much of their stuff was interchangeable -- any Jackie, Tony, or Morty with a tuxedo and a sense of timing could do it. But that changed when the likes of Robert Klein, George Carlin, Richard Pryor, and David Steinberg came along. Suddenly, the joke wasn't as important as the joke-teller. None of the material Pryor did would have worked for Carlin, and vice-versa. Elayne Boosler and Joan Rivers couldn't do the same act. Neither could Jerry Seinfeld and Bobcat Goldthwait.
A couple of nights ago, Ray Romano appeared on Arsenio Hall's show. They're about the same age and know each other from their years struggling to make it on the comedy club circuit. So, as a gag, they did a segment in which they did each other's old routines, and it proved my point about how important it is to have your own voice in comedy. The interesting thing was how much better Romano's timing and performance were than Hall's. The latter looked like he was reading something he'd never seen before off a teleprompter, and the material suffered from his poor delivery. Meanwhile, the former not only knew the lines, he performed them perfectly.