Here is a question/answer from Paolo Bacigalupi from Fantastic Reviews:
R: You have pretty high standards if you're feeling that way about your stories.
PB: Well, I think there is compulsion there, too. Right now, I'm working on this novel of mine, and I have a horrifying number of first chapters. And I look at those and I think, this is obviously a sign of a crazy person. You can't have this many different versions of a first chapter and see anything other than insanity at work.
But the other thing that's going on is that I'm not clear. And that's why I keep writing these versions, because I haven't come to that one that says, right, I know what I was trying to say. So I know the reason for that compulsion is I'm hunting for something that I can't quite articulate even to myself. Sometimes I'll try to mark down, these are the things I want in this. I want this element or I want this character to be able to do these things. And I know those are there, but there's something else more intangible that just says, no, that didn't quite nail it; it just doesn't quite fire on all cylinders for some reason.