This is from the Paris Review Spring 1956 issue, an interview with William Faulkner:
INTERVIEWER
Is there any possible formula to follow in order to be a good novelist?
FAULKNER
Ninety-nine percent talent . . . ninety-nine percent discipline . . . ninety-nine percent work. He must never be satisfied with what he does. It never is as good as it can be done. Always dream and shoot higher than you know you can do. Don't bother just to be better than your contemporaries or predecessors. Try to be better than yourself. An artist is a creature driven by demons. He don't know why they choose him and he's usually too busy to wonder why. He is completely amoral in that he will rob, borrow, beg, or steal from anybody and everybody to get the work done.