This is the part that I doubt will ever be achieved by any system or structure of moderate complexity or above. Everything that exists in the real world has problems with it. If it's a building or a machine, then it's done once it's built unless there are major safety issues. The cost of fixing non-critical issues in a physical product is too high to justify.
The problem with software is that the marginal cost of "one more fix" is close to zero, which means that declaring something "done" means drawing a somewhat arbitrary line in the sand. Why is this new complaint less important than the similarly-scoped one that you fixed last week? There's not really a good answer to this question, so there's never a good day to say that you're not fixing anything more.