You can keep working on this arrangement forever. Improving it, tweaking it, honing it.
(for “arrangement” read “painting”, “monologue”, “song”, “short story”, etc….)
But it won’t be your last arrangement. It doesn’t need to be the ultimate representation of who you are as an artist.
Finish it, put it into the world, and learn from it. Then start another one with the lessons learned.
This is one of the many reasons I like conducting a choir – there is always a drop dead date of a performance; you’re going to perform it December 18, ready or not.
I’ve tried to apply this mentality to my writing as well. Print it, distribute it, and move on.