How much of a book is in your mind before you start?
What matters most isn’t there at all. I don’t mean the solutions to problems, I mean the problems themselves. You’re looking, as you begin, for what’s going to resist you. You’re looking for trouble. Sometimes in the beginning uncertainty arises not because the writing is difficult, but because it isn’t difficult enough. Fluency can be a sign that nothing is happening; fluency can actually be my signal to stop, while being in the dark from sentence to sentence is what convinces me to go on.