What makes screenplays difficult are the things that require the most discipline and care and are just not seen by most people. I'm talking about movement - screenwriting is related to math and music, and if you zig here, you know you have to zag there. It's like the descriptions for a piece of music - you go fast or slow or with feeling. It's the same.
Robert TowneThe one thing you know when you're shooting a script - and I've been on a lot of sets - is space is in a script, and the distance between the page and the stage is so enormous that it is unbelievable how even the brightest people can misread your intent or not see it altogether. Scripts have air in them. Scripts are supposed to leave things up to interpretation, but people can misread things enormously, so sometimes it's just a matter of wanting to put on the screen what you had in mind.
Robert Towne