From Paul Graham:

“One of the most interesting things we’ve discovered from working on Y Combinator is that founders are more motivated by the fear of looking bad than by the hope of getting millions of dollars.”

From Jimmy Connors:

“I hate losing more than I love winning”

It’s counter-intuitive, but I think history has shown that fear is a more powerful motivator than greed and/or ambition.  I can’t find the quotes, but I think I recall reading multiple biographies of Michael Jordan that suggest that his biggest motivator is his hatred of losing. Anyone who has seen Tiger Woods in the flesh can probably vouch for the same thing.  They play for the love of the game, but they are great competitors because they are afraid to lose.

What motivates you?