When is finished really finished?

Thankfully the weather was great today and the roof repairs are finished. I have a quiet(ish)* house again. Today I also 'finished' my latest edit of 'The Land Beneath the Shadows'. However, I find that I am feeling a little envious of the concrete and definite completion a job like roof repairing has. It is clear to everyone who looks if a house has a roof on it or not. Once the roof is secured, the job is done and you can leave and go onto the next house. For me, it's never that clear that a book or story is finished. There is never one final nail that you can bang in and then know with total certainty that your story is finished. It always feels that I could creep back into the story, tinker a sentence here and there, maybe change a scene or two. There is always the sense that maybe you could find something to polish, alter, take out, put back in or rearrange in the never-ending pursuit of making the story even better. There might always be something you could do, some finishing touch that might make the story perfect. I have never yet got to the point where I felt that the story was perfect. I've never had the smug happiness of knowing that a story is finished and improvement is impossible. So that's my big question: when is editing finished? How many drafts and rewrites does it take before you're done? How do you know when to stop and send the story out into the wide world? Is there a process, a method or a feeling that tells you when it's time to let go of the editing and put your 'finished' story out there? * Once you have children your home is never really completely quiet but the excited sounds of an enthusiastic toddler rampaging is peaceful compared to the noisy, disruptive banging and thumping.