Working at Writing

"I want to be able to convey the idea I have in my head right away, and that just doesn't happen."

My roommate said this to me tonight. She's sent me some sketches of hers to look over and critique, which led, of course, to a discussion of writing in general.
I read somewhere that Tolstoy said nothing is worth reading until it has been revised a thousand times. If Tolstoy felt that insecure about his writing, then my need to rewrite is probably somewhere near a trillion. That's precise mathematics at work, people.

I credit my aversion for rewriting with the meagerness of my portfolio. I've written very little. When I do write I find it hard, nearly impossible, to make substantial changes to a "finished" piece. Maybe the years of writing essays for classes, the sense that when something is handed in, it is for all intents and purposes formed permanently, have hardened me into a routine of non-revision. Whatever it is or was, I don't rewrite. And so I don't write. If I can't at once leap to what is in my mind, I give it up for lost.
I wonder what would happen if I didn't?