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 tried the paleo diet, which is the caveman diet - lots of meat. And I tried the calorie restriction diet: The idea is that if you eat very, very little - if you're on the verge of starvation, you will live a very long time, whether or not you want to, of course.”