The Other Question: When do you know it's finished?

This is an addendum to the last question: "How Long Did it take you to paint that?". And so, when DO I know when a painting is finished? My teacher, Paul Rahilly has said; unless you are from Finland, a painting is never finished (Finnish). However as an artist one does have to know when to stop working and changing a painting. My own personal guideline is internal; when the painting makes me smile, I know enough to stop working on it. On another level I also carefully and mindfully keep painting,changing and evaluating what I am doing with the paint until my efforts no longer make the painting any better. The painting above is still taking longer than I thought but every time I get to work on it, it is getting better and closer to the exciting painting I had in mind when I started. Now, back to work.