As long as a film stays unmade, the book is entirely yours, it belongs to the writer. As soon as you make it into a film, suddenly more people see it than have ever read the book.
“I think most people read and re-read the things that they have liked. That's certainly true in my case. I re-read Pound a great deal, I re-read Williams, I re-read Thomas, I re-read the people whom I cam to love when I was at what you might call a formative stage.”