Good books write themselves, and this can be said from a small but successful book like Ripley to longer and greater works of literature. If the writer thinks about his material long enough, until it becomes a part of his mind and his life, and he goes to bed and wakes up thinking about it—then at last when he starts to work, it will flow out as if by itself. A writer should feel geared to his book during the time he is writing it, whether that takes six weeks, six months, a year or more. It is wonderful the way bits of information, faces, names, anecdotes, all kinds of impressions that come in from the outside world during the writing period, will be usable in the book, if one is in tune with the book and its needs. Is the writer attracting the right things, or is some process keeping out the wrong ones? Probably it’s a mixture of both.
From Patricia Highsmith, Plotting and Writing Suspense Fiction (1983).