When Does Revising End?

It feels like I could revise/rewrite my screenplay forever. It never feels finished. I guess that's what Lapadula mentioned in class, that there is no such thing as a perfect screenplay. But the tricky part is knowing when to quit rewriting and just call it done. I don't really have a sense of that, maybe it comes with experience. But I keep going over my screenplay and I keep tweaking this, changing that, deleting this, rearranging that, etc. It kind of feels like when I'm editing film, too. I used to film random movies in high school, and whenever I got to the editing part, I could spend 10 hours a day for a week doing editing, cutting scene lengths, adjusting transition times, working on supers, fixing the sound, choosing takes, etc., and still continue messing around. Even when I look back now on films that I had already pronounced finished, I feel like changing things, re-editing. Whether it's screenwriting or editing, I can't seem to be able to find a sense of when to stop and feel, if not satisfied, at least satisfied enough.