I have a problem, like most writers I think, of not wanting to let go of a story. It's why I spent eight years working on my first novel and still sometimes think about going back to it. It's hard to let go of something you're passionate about. But sometimes it's necessary.
Sometimes we get so wrapped up in a project that we get feedback and suggested improvement and we desperately try to make them work, even if it changes the story we're trying to tell. Sometimes we get so obsessed with the story that we refuse to see it isn't actually salvageable and spend months or years trying to fix something that has a fundamental flaw we're willingly blind to.
That is how we as writers don't finish anything. That's how we shoot ourselves in the foot where a writing career is concerned. If we spend forever trying to perfect a story despite knowing that it isn't working on some level, or if we simply spend too much time polishing it in an attempt to make it as pretty as we think it should be, we never get our work out there.
There's no hard and fast rule of when you should set aside a project, unfortunately. I'm struggling with that right now. I've been working on a short story for a (now defunct) magazine for the last few months. It's gone through three or four rewrites and just ran through critique group again last night, which basically brought up the fact that I haven't fixed the fundamental problem in this story yet. I keep going back and forth as to whether I should keep going with it and find somewhere else to submit it, or just toss it in the trunk for now and move on.
It's a tough call, and one that doesn't really have a right answer. The only thing I can say for certain is that we all need to make sure that we're actually finishing things!
Emily is really bad about obsessing over things. She just wants her stories to be perfect, dang it! Of course, she also knows that's not actually possible.