I don't have a specific moment when it happened, like heatray does. However, I can remember when I realized there was a possibility.
I've always been a 'leader' in my social group, no matter how big or how small the group. However, in college I was always the reluctant leader. I'd take control of situations out of frustration, and when things were running smoothly, relinquish it to the popular and egocentric.
It wasn't until college when I realized that my opinion meant something to people. I can remember sitting at dinner with my best friend and saying, "Hey, did you realize that you and I determine who is popular and who is cool in our social circle now?" And once I realized it, and realized that it wasn't just a fluke, I realized that hey, yeah, maybe I *DID* have something valuable to offer people. Maybe I *COULD* take control without having to do it just because no one else could.
And now I can shape my own world.