Smoke and Mirrors

I'm just curious... I've started a new painting and whenever I start a new painting (or drawing) at some point I look at it and think, "Ohmigawd, this is crap!"  But a little voice inside says, "just keep going..."  Invariably, it turns out fine, but there's always that beginning critique given by my inner self.  Does anyone else go through this?  And if so, why?  Why does this happen?  I'm just curious...  

I'd love to hear from others on this.