Come for the code, stay for the community
Two years ago, I hesitated at the door of a meeting room at DrupalCon Chicago: Drupal 7 Module Upgrade Sprint. I had a module that needed upgrading, but only a vague idea what a sprint even was.
I sat down near two people who introduced themselves as Peter and David. They asked me what I was working on and helped me feel less out of place. We talked about Drupal 7 and their jobs at Acquia, and through their acquaintance I got to have lunch with Drupal 6 maintainer Gábor Hojtsy as well.
The encouragement I received at that sprint changed my life.