Gail Z. Martin
Well, the short answer is--contract deadlines! The long answer is that the clearer the picture of the next chunk of book is in my mind, the faster I write. If I have to stop and figure things out, fact-check, look things up, etc., I write a lot slower until I get that clarity. With due dates, you can't really wait for inspiration to strike--you have to be able to kickstart yourself.