[My son Sean] tells me his trouble is that he gets part way into the story and then thinks "This sucks" and stops writing. I told him, "Do you know what that makes you? An absolutely normal writer. The trick is not to let the bits that suck make you give up on the whole thing. That's the great thing about writing. You can go back and make it something else right up till the moment they publish it."--Mark Shea.
Now I just need to apply that advice to the project I've been struggling with for the last while.