There is a difference between pursuing excellence and pursuing perfection.
Perfection is unattainable–no matter how much more time and effort go into the project, there will always be something else that could be done. You may inch closer to perfection, but you’ll never actually get there. Excellence, on the other hand, is attainable. And as such, it should be the target.
The challenge is to know if we’re still pursing excellence in a given project, or if we’ve already reached it and are now pursuing perfection. To stop before achieving excellence only weakens our body of work. But to push on for perfection after this point only results in fewer and fewer results for the time we continue to spend.