"...The process of writing a screenplay is different from writing a play in many essential ways. The first is the difference in the use of action.
For screenwriters, action is the primary tool of structure. But for playwrights, the primary tool is dialogue.
Don’t get me wrong. As a playwright, you need to visualize to some degree what is happening on the stage in order to really create your dialogue, in order to create the piece. But you don’t have to communicate that to anybody else. People don’t need to see your play in their mind like they do when reading a screenplay; they need to hear it, and they need to see the big elements.
You get to rely on the director, because plays have this thing called rehearsals.
It is crazy that rehearsals, for the most part, don’t exist in filmmaking. Even though some of the really great film directors do rehearse-- for example Francis Ford Coppola had a history of bringing the cast up to his estate to rehearse-- most film directors don’t rehearse at all.
That’s for a very simple reason: stars cost about $20 million bucks..."