A book that's "good" enough to be made into a movie is popular and well-known. I don't think they would make a movie on a book that isn't New York Times Bestseller. They could be classics like Jane Eyre or just fads like Twilight. Either way, they very rarely make good adaptations of the novels. When you write a novel, it's written in blood, sweat and tears. With writing you create, with filming you're just changing the story to a different media. I'm sure it's hard work, but it's just not the same as writing a novel. Then again it's all pretty subjective. I mean, Pan's Labyrinth was awesome and that has blood, sweat and tears written all over it.