I sew clothes. The vast majority of projects I start get finished. Sometimes I'm happy with the result, sometimes I'm not. I wear them regardless. My kids wear them. After a while they grow out of them.
Goal achieved, project finished.
Good point about being happy with the results! I think this could be added to the definition of success.
Some results can not be improved, like sewed clothes, but there can be a review to learn something (why are you not happy with the result?) and a feedback loop, for the next project to turn out better.