“One of the hardest parts of being an artist is that there are no rules. You put marks on canvas and then react to and revise those marks, guided by intuition and experience. A work can be called “finished” at any point in this process.
It takes courage to call a painting finished and signal that you’ve done all that you can with it; the painting will stand as the embodiment of your ideas and painting skills at the moment of completion. Yet finishing a painting can also be liberating: It creates space for new ideas and experiments to begin.”
This article from Artsy (by permission) offers hints to finish–and know when you’ve finished–an artwork.