I think at some level, it's just alchemy that we, as writers, can't explain when we write the characters. I don't set out to create the characters - they're not, to me, collections of quirks that I can put together. I discover the characters, instead. I usually go through a standard set of interview questions with the character in the beginning and ask the vital stuff: What's important to you? What do you love? Hate? Fear?. . and then I know where to start. But the characters just grow on their own, at a certain point. And start surprising me.
When you make movies, I find that I never have time to go to the movies and enjoy movies like I used to, because I'm so movied out, right, I'm so filmed out that the last thing that I wanna do is with the little spare time that I have is stick in a dark room and watch more stuff on the screen.