A frequent question for writers: How do you know when a piece of writing is finished? One famous reply to that question: when you put back in the same periods and commas that you just took out.
My own experience, just recently, has to do with "bogs." That is, those morasses that writers sink into when trying to make their work perfect or, let's be frank, invincible. Standing up against any anticipated criticism. So here's an example.
I just wrote a story and one of the sentences that I kept trying to work in was "Janice could almost be alive in Las Vegas." I'll skip the story summary; in fact, I'll skip any context, and just tell you that I worked with this sentence, with some coffee and bathroom breaks in between, for 3 hours, a long time for one sentence. I tried rephrasing it: "Janice, Gene realized, with stinging regret, could almost be alive in Las Vegas" and "Janice, Gene realized, with stinging longing, could, in this city of might happen, almost be alive out here." But wait! It changes everything when I use an em dash: "Janice--he realized with stinging longing--could almost be alive out here."
If that wasn't enough, I tried it in parenthesis; in a paragraph by itself; as part of another sentence; at the top of the page; at the bottom of the page . . . you're perhaps getting the point. What I wanted from this sentence wasn't possible. I wanted it to "explain" the story, that is, bring all the ideas, subtext, conflicts, themes to a head and make it the zinger that would perfect the piece.
But of course this is impossible, and happens when the ego gets too involved in trying to make the story's meaning foolproof. So much stress is put on the revision process to make a story "fully realized" that one often pursues a quixotic search for readerly clarity at the expense of, if I may, a story's confidence. The story has to have confidence aside from the author's own intentions or wishes for it. Such confidence necessarily requires a certain degree of ambiguity that actually lends the story authority. Once you start searching for the definitive sentence or paragraph, the ultimate line of dialogue or story's final word you can be pretty certain you have lost the initial thread that allowed you to subordinate and proportion all the complicated fiction elements in their proper places. Yes, Mark Twain memorably said that the difference between the right word and the next to right word is the difference between lightning and the lightning bug. But the right word has a spark of spontaneity and grace to it; the perfect word has a whiff of sweat and pushiness.
In other words, you need to back off and let the narrative take its chances. This is not overwriting, for who knows when that is exactly, as much as clinging, and you'll feel it in your body as a slight revulsion. You're in a bog and struggling to get out. Stop flailing, turn off the power to your computer, take a walk, wait twenty-four hours, reread the twenty drafts of the obsessive line, word, or passage and then watch how easily it peels away like a fatty tumor. And what have you lost? Nothing. And was it necessary? Yes. You'd have no way to know otherwise.