Er. Realize this thread has been quiet for awhile now, but I had a thought on it. So I'll quack into the void for a moment, and then life can resume.
I think the dangerous thing about understanding that you have a million or so words of crap that you'll write before you write your good stuff is, it can feel like a "Get out of jail free" card. It can b ea trap.
I knew a guy who liked the advice and spent a long time writing slop stories because, as he figured it, he was just slogging through the lousy stuff before he would start to shine. Problem was, he wasn't slogging enough and was more or less just floating. A million words later, still crap but from a more frustrated miserable writer.
Everything you write is a diamond, is a miraculous story that will reshape your world and resonate brilliantly -- perhaps violently -- through your reader's soul. It will move them, it will perhaps scare them, and it will be the greatest piece of English literature, and you should damn well believe that when you write it.
If, ten hours/days/years later when the embers have cooled and it is no longer your Darling, if you look at the story and understand that it is crap...fine. But it was a footstep along the road anyway, so not all lost.
While writing, though, treat your story like it is what the English language was made for.
This concludes my quack into the abyss. Please resume your regularly scheduled lives.