Most people don't know how ambitious to be. They don't know what's hard, or what they're capable of. And this problem is exacerbated by having few peers. Ambitious people are rare, so if everyone is mixed together randomly, as they tend to be early in people's lives, then the ambitious ones won't have many like-minded peers. When you take people like this and put them together with other ambitious people, they bloom like dying plants given water.

—Paul Graham