Build something you personally want and need...I guess that fits under passion, but there's something especially rewarding about building something that actually makes your own life better, after it's built.

Good post! I always tell people if they really want to make money, go work on Wall Street. Doing a startup is quite a bit riskier. For me, it's really about doing something meaningful that I enjoy. Here's a tip I read that I really like, two things you might want to ask yourself before doing a startup: a) if you're rich already, would you still do this? And b) if you can't fail at what you do, what would you do. http://yana.com/tips/80

Economically, you can think of a startup as a way to compress your whole working life into a few years. Instead of working at a low intensity for forty years, you work as hard as you possibly can for four. This pays especially well in technology, where you earn a premium for working fast.

http://www.paulgraham.com/wealth.html

For me it is altruism

I figured I'd learn more doing a startup than heading into another Wall Street job, where I'd be seen as "below" the people with PhDs and years of trading or programming experience.