I guess I'd never really given it much thought, but I'm glad to hear others are motivated by insecurity, proving others wrong, etc. The first company I ever built was when I was 15, to this day I remember a conversation I had with my dad explaining an idea "I'd heard about". In reality, I'd already built it, but his response was something along the lines of "that sounds like a terrible idea, and it's probably not legal". It hurt, and he probably wouldn't have given that appraisal had he known it was my idea, but it made me want to prove him wrong. A year later, he was managing sales at my company while I went to high school during the day.
All these motivators seem like emotional instabilities, is motivation really internal at all? I wonder, what if I hadn't been told my idea sucked, would I have had the same drive to make it work?