Most of my former and present clients are high-tech junkies: they can't resist founding another startup no matter how much they cashed out for the last startup or especially if the last startup went bust. Some people just get high on high-tech startups the way addicts get high on drugs. And there are lots of similarities, from creating a reality away from reality to running at full speed all the time.
Startups -- like drugs -- give life purpose, and whereas 1,000 years ago joining a monastery or a marauding pack of knights might have evoked the same high, today's technology allows those in pursuit of conquering the world through new tools and memes a more harmless high.
If I were a psychologist, I would say that most of my clients want recognition, and that's a driving force for their entrepreneurial pursuits. Most people with a good idea don't take the next step to start a company. Larry Page and Sergey Brin could have created their search algorithm by writing a Ph.D. thesis at Stanford and publishing it, but instead they started Google. What drove them to start a company when they could have become distinguished scholars?
I don't think money is a great motivator for people who do start-ups. Most of them could earn more money becoming realtors or funeral directors, and they'd certainly need to expend less effort. Money might be a distant end goal, but the process of starting and running a company consumes so much brainshare that recognition and adoption rather than enormous wads of revenue become the main goals.
If you were to ask Facebook founder and CEO Mark Zuckerberg what he's going to do with all the money he's making, he'd probably say that when he has the time -- say in 10 years or so -- he'll figure out how to dispose of it. But by then, he'll be onto his next startup, the way Mosaic/Netscape founder Marc Andreessen went onto his next two startups and then became a funder of startups.
Maybe it's human nature. It's like a love affair -- far more fun to start than to continue and eventually end.