One of the trickiest things about making a new piece of art can be knowing when it's finished. And there are usually two voices weighing in on when this point has arrived. One is my logical, thinking brain, the other is my subconscious mind. It is nice to operate with both, but I have found that my intuition is right more often. I think this is in part because my subconscious mind is always ahead of my conscious mind. So, often, when I listen to my gut feeling, even if I don't understand it logically, later on I will be pleasantly surprised when my thinking brain catches up and can say "Oh, I see. This is why it was finished." Or, "This is why that piece of paper or splash of color looks good there."
I just finished a new book cover yesterday. I feel good about it. But if I gave my analytical brain a chance, it would like to keep working it to death. But, I know that it is done, so I'm choosing to let it be.