Joel Coen

When an actor improvises a line on the set, he will almost invariably say something like, "That was great, but could you do it like it's written in the script?" Most Coen brothers films are the same (line for line) when released as they are on the page in the final draft of the script.

Frequently we are writing characters and we are thinking, "Wouldn't it be interesting to see such and such play this kind of a person?", and the character starts to grow out of that as you are writing it. It's a combination of things that you are making up and what you know about the actor.