Ask HN: How do you 'finish' your projects? 15 years ago
A product is never really "complete". Your personal "completion" date will be when the responsibility for support, modification, and enhancement is transferred to someone else. There will always be room for improvement in any product, but we all need to eventually step back and see where our efforts will have the greatest value.
Eventually, there will be a new unit of work for you to tackle with a bigger payoff for your time. The transition is not instantaneous... gradually, that new project will consume more of your energy, until it becomes your main focus.