Free time. When I've no urgent household tasks to do and I have four hours ahead of me, I know I can dedicate time writing if I need to.
When I'm writing Hell 2.0, my current project, I have a notion of what I want to happen in the plot, but the characters personalities drive the action. I tell people it's a bit like being an embedded reporter that is merely relaying the action.
In dreams, we all know our brains make up the stories we participate in, but we aren't consciously causing the events to happen. Writing, to me, has been a lot like that. All my characters have personalities. There is a limited number of ways they will react. The favorite parts of writing the novel are when my characters react naturally to the events unfolding and yet I didn't foresee what they would do until I'm typing it. Just like in dreams, your own brain can surprise you.