When is it Done?

Q. You start off the "How To Make Webcomics" book briefly touching on the attribute that a lot of artists seem to have. It's the "I'm not good enough" syndrome. Well after battling this through my life I set it aside to start the webcomic but now I find it creeping back again. I draw a strip and immediately want to redraw it knowing that I can do better.
How have you guys gotten past this and when do you know that the strip is ready to publish?
