Short version: success spirals.

Long version: I started by putting together small events for fun. It was originally in the easiest context imaginable—Boston's LW community had a bunch of people who explicitly wanted structure at the meetups, but no one to reliably organize things. I made some games happen (zendo and a prisoners' dilemma tournament come to mind) because I wanted to play. When those went well, I put together a tabletop gaming group outside of meetup hours.

At first, telling people what to do was scary and I felt presumptuous, but that faded after positive reinforcement. I had fun playing the games I'd chosen. People thanked me for making cool things happen, and I got shiny status points. I saw that cool things happened when I made them happen, but cool things didn't happen when I didn't make them happen. I got to declare that a thing was true and then see it become true and it felt like being a motherfucking sorcerer.

After I ran Schelling Day, I was asked to take on responsibility for organizing the meetups. That's when I explicitly took on the "good at making things happen" identity and started acting this way by default. I use this to motivate myself to do anything that seems scary, and to overcome the bystander effect:

"Why aren't we going to dinner yet? I'll get people moving, since I'm good at organizing things."

"Everyone here said they'd like to play more improv games, but no one is playing improv games. I'm good at organizing things, so I should make that happen."

"I have no idea how to plan a megameetup, but I'm good at organizing things, so I'll be able to figure it out."

As I succeed at more and more ambitious things, this gets stronger and stronger. Right now, I'm looking at how to make a career out of it.