My friend Rachel Cornell writes an interesting blog about human nature and the sometimes puzzling aspects of our behavior http://pronagger.com/. She recently polled some of us about how we determine when a piece of artwork, writing or other creative endeavor is declared finished. I contributed a few paragraphs in response, but I admit I don't really know how to answer the question definitively. I nearly always see some flaw or unresolved issue in my work. It may just be the obsessive traits within me but I usually regard work finished only if it is gone and I can't get it back to work on.
That said, the above painting was returned from a gallery and after 9 months I wanted to improve it. It's done now.
What's re-newed: Beginning Anew, oil on canvas, 39"x39"