Writing, that is.
It’s a job that you mostly do sitting at your desk, listening to the voices inside your own head. It’s not surprising that some writers end their careers as eccentric hermits; what’s surprising, actually, is that more of them don’t.
It isn’t required to be an introvert in this job, but sometimes it helps. At the same time, if you’re going to make a living (or at least a part of your living) as a writer, you’re going to have to get out in the world. If you don’t, you’re going to lose touch with all the stuff you’re writing about.
So make the effort. Schedule time for things like community involvement — things like scouting, or the volunteer fire department, or the folks who clean up sea birds after oil slicks. Whatever works for you, so long as there are other people involved in it. From an artistic-development standpoint, it helps if it’s the sort of group that attracts a cross-section of different types, so that the repertory company of actors living in your brain can have as wide a range as possible.
Don’t isolate yourself from other writers, either. Some days, it can be vitally important to your sanity that you’re able to have a conversation with somebody else who understands why it is you do what you do with all those words on the computer screen, and who understands why it matters.
Which is why I’m moving mountains, right this minute, in order to be at Readercon this weekend, down in Burlington, Massachusetts.