The movie Social Network tells us the story of Facebook, how it is founded.
The thing is, no matter if the Winklevosses are right or wrong, it really took too long for them to build and activate the social network site. They have a cool idea but they just can't make it real regarless of their excuses. Mark Zuckerberg, on the other hand, builds the entire site in like 2 months, doing almost everything by himself.
Bottom line here is: he does shit, not talk.
Zuckerberg is a genius, or at least this is how he is portrayed in the movie. So he has an advantage in that. But honestly, i really don't think you need to be a genius to make a site like Facebook, or at least the one in its early forms. Obvioulsy enough, you need to know coding, or you will have to stuck with other people who knows coding and who can steal your idea or who can stall you like forever.
This is how things are run in real life too. Many people have a cool idea. But they don't really do much to make them real. It is not like all of them will become the next billionaire, but at least they do something. And the others, they just wait.