In a recent interview, Google's CEO, Dr. Eric Schmidt, had this to say when asked about the characteristics of very successful entrepreneurs:

I think the most important characteristic of an entrepeneur is that they’re going to do it whether you give them permission or not. They are motivated by something inside of them. It’s not something that can be taught... they feel it, they want it, they’re driven to it. And when you find such a person, they’re usually a pretty good person to hang out with. They’re gonna do some interesting things.

Reminds me of something John Doerr said to the folks at the Cleartrip office--"To ask permission is to seek denial."