I'm sure I've said this before, but experience is teaching me how true it is.
Finish what you start writing.
It doesn't matter if it's a lousy first draft with terrible characterization and a sappy ending. What's important is that it's equally lousy throughout.
If you don't finish, then you get a hunchback of Notre Dame kind of monster where parts are extremely overworked and polished, and parts are spindly and lousy, and parts are just missing, and who wants to attach garbage to fine jewelry? It's paralyzing.
Nope. Better to puke the whole mess out at the start and work on cleanup later when you can stand to look at it again.
That's not really the best analogy, since most people don't make sculpture out of vomit, but it's the best I can do this morning.
Finish what you start.