Umair Haque wrote recently that the reason there aren't more Googles is that most startups get bought before they can change the world.
Google, despite serious interest from Microsoft and Yahoo—what must have seemed like lucrative interest at the time—didn't sell out. Google might simply have been nothing but Yahoo's or MSN's search box. Why isn't it? Because Google had a deeply felt sense of purpose: a conviction to change the world for the better.
This has a nice sound to it, but it isn't true. Google's founders were willing to sell early on. They just wanted more than acquirers were willing to pay.