I found this gem from an interview with Eric Schmidt, the CEO of Google:
Q: Talking before, you’ve spoken glowingly about Larry and Sergey, and also Chad and Steve from YouTube. What are the characteristics of very successful entrepreneurs?
Eric: I think the most important characteristic of an entrepreneur 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. In Larry and Sergey’s case, and more recently with YouTube with Steve and Chad, they were going to be successful, and you can tell when you talk to them. Everything else is a tactic compared to that passion and vision that an entrepreneur has. It’s relatively rare, and it’s important to identify and respect it. (…)
(read the rest of the transcript)