This is an edited version of a comment I originally posted on the Passive Voice blog.
Writers get far less respect in the movie world than written fiction. Yet many are happy to work for free to get any kind of credit, and hope they actually do get their credit at the end.
There’s a big difference between novel writing and screen writing. If you have an unpublished novel, you can at least show it to your family and friends, whereas if you have an unproduced screenplay they probably won’t even know how to read it. The only way for a writer to prove they can write a movie is to write a movie that’s actually produced.
The other issue is that the screenplay is only the beginning of the work. Once it leaves the writer’s hands, the actors will improvise and the director will change lines or rewrite whole scenes. When the shoot is complete and the movie is just a bunch of files on a computer, the editor will cut lines, move shots around or even cut entire scenes which don’t work. The director may record new off-screen dialogue or some extra shots to fill in plot holes.
So by the end of the movie, it may bear little resemblance to the original screenplay. After many other people have interpreted it and revised it, the writer may justifiably be unable to take much credit for what finally reached the screen. In my case I take no credit for the ending of the one feature-length movie I wrote which was actually produced because the director threw out my wonderful ending and replaced it with his own.
By the time the premiere rolls around the writer thinks the director is a dick for rewriting their screenplay, the director thinks the writer is a hack because they had to change so much to make it work and the editor thinks the writer is self-indulgent because he had to cut out half the dialogue and the director is clueless because he had to spend six hours looking for any two shots he could cut together to make the final scene work.
Which has given me a good idea for Horror Movie. Damn, got to rewrite part of it again.