but like all other things, they start from one person.
To quote Seth Godin, (since I can't put it any better than he did)
My favorite part happens just before the first minute mark. That's when guy #3 joins the group. Before him, it was just a crazy dancing guy and then maybe one other crazy guy. But it's guy #3 who made it a movement.
Initiators are rare indeed, but it's scary to be the leader. Guy #3 is rare too, but it's a lot less scary and just as important. Guy #49 is irrelevant. No bravery points for being part of the mob.
We need more guy #3s.