While not the best advice to give an alcoholic, the spirit of the phrase is a great way to defeat writer's block.
Not all of your prose will magically flow onto the page in perfect order. So just write something, the crappier and more senseless the better. You'll find it self-correcting, starting to flow. Go with it until it seems like you're forcing things. Then stop.
You can always cut and paste later, move it around. Read it out loud and say to yourself, "wow, what was I drinking?"
Just show up at the page.
