Joan Rivers reckons that being "totally insecure" is the main reason why she still wants to stand up and make people laugh in her mid-seventies.
The US star also revealed that it is the comedians who "go too far" who really make her laugh.
Asked about the secret to her staying so active, she said: "In truth, there are three things I put it down to. I love my work, and I think that's a big thing. That's where the enthusiasm comes from.
"Number two, I'm always working on new projects that excite me, and number three, I'm totally insecure. That's probably the biggest one."
The comedienne said she worried that her faculties may let her down "every single day", adding: "But right now I'm on stage and everything is going great and I don't see any variation so it's all good.
"It's strange and wonderful, still being here. I never thought about the future. I've never had the chance to say, 'gee, I wonder how much longer this will last'?"
Asked which comedians make her laugh, she said: "The ones who go too far. I love Little Britain. My jaw hurts. Ali G, I go nuts for him. It's the naughty ones.
"I love things that make people say, 'oh my God'. It's the body of work that makes you go 'wow'.
"People ask me if I wish I had come along a few decades later. I don't know. I think maybe the reason the comedy scene is like this today is because I was doing the equivalent of it in the beginning."
Joan Rivers: A Piece Of Work is available to buy on DVD.