You can do everything differently in a novel. Hero narrates the novel; we're in his head. You're hearing all his thought processes and you're hearing him call himself out on his bad behavior. You don't have the benefit of that narrator in a movie. What you see a character do, very often, becomes that much more important because you don't have him editorializing it for you.
Screenwriting you don't necessarily have to do the job of the costume designer and the prop master and the set designer. It's more just about finding the visuals and finding these characters through dialogue.
Novel writing, to me, is all about language: choosing your words, finding the characters within the words and just really agonizing over every word. It's really crafting this whole piece from nothing.
When I'm writing novels, even screenplays, it's never an actor I have in mind; it's always the version in my head of who the character is. Once somebody gets cast, I have to adjust a little bit to who they are.
It's sort of an organic process when you're adapting any book, not even just your own. You want to preserve the heart of the story and you want to preserve who the characters are, but film requires a lot of compression.
