It rarely takes more than a page to recognize that you're in the presence of someone who can write, but it only takes a sentence to know you're dealing with someone who can't.
(By the way, here's a simple way to find out if you're a writer. If you disagree with that statement, you're not a writer. Because, you see, writers are also readers.)
— Scriptwriter John Olson, 'I Will Not Read Your Fucking Script'