Everybody wants to be a screenwriter. They all sit and look at movies and after they've seen so damn many of them, in the theatres, or on TV, or on videotape, and they think, 'This is easy—I can write a film!'
This applies to your cook. Your dentist. Your garage mechanic—they all say, 'Hey, I've got a great idea for a picture,' and they come to me and they say, 'I've seen movies all my life, and how would this be, here's an idea. And I say, 'It would be bad, it would be corny, you've seen it up there on a screen before, it wouldn't work, trust me! ... But they don't.
What causes such arrogance? Their lack of respect for the craft. People do not realize—writing a film is very difficult. They do not realize that you must serve your internship, that you must develop a feel for it. And, additionally, you have to learn the mechanics! It is a craft that has to be learned!' ~Billy Wilder, 1972