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.
“You know, my family and friends have never been yes-men: 'Yes, you're doing the right thing, you're always right.' No, they tell me when I'm wrong, and that's why I've been able to stay who I am and stay humble.”