What do you do? How do you fight that self-damning urge?

In no particular order, my coping mechanisms include: crying, whining, yowling, angsting, complaining, and wallowing in doubt/depression/despair.

I think such doubt is part of the creative personality. Over time, though, I have learned to trust my instincts as a writer more and more, and the above mentioned coping mechanisms have lessened. :-)