There are two broad categories of revising:
-Changing big things, like structure, character motivations, etc
-Changing little things, like "dark" to "gloomy" or maybe "dismal"
You can absolutely get trapped on the second thing, constantly adding or removing commas or picking a slightly better word then changing your mind later. You can polish and polish and polish and try to get to "100%," but that's impossible, because art is subjective, so you are never going to make every single person who reads your story happy, and that includes beta readers. And that includes yourself, too.
You need to be mindful of what kinds of revisions you're doing, and if it's really accomplishing anything. In an ideal situation, you have had multiple beta readers, you've put your ms down and come back to it a month or more later, done a few rounds of editing, and done your own round of line by line editing. So all that big things have been fixed and you've done the best you can fixing most of the little things (and hopefully all of the "objective" little things, like spelling mistakes, forgetting a period etc). But if you're in an endless cycle of revising the subjective little things, you are never going to be finished.
Say you're an engineer and you have to make a car that goes 100 miles an hour (pretend this is before cars went this fast). A lot of hard work is going to get the entire car designed, and you end up with a car that goes 80mph. You go back and redo some things, and now it's 85 mph. But if you totally redo the tires, you'll get another 5%. A spoiler on the rear gets a couple more mph. But once you get to 95 mph, everything left you could possibly do requires a TON of effort for only an additional 1 mph, maybe. Redesigning the whole thing to be lighter takes a lot of work, you need to use new materials, you need to re-tool a bunch of stuff at the factory, you'll have to re-certify all the safety tests. Is all that time and money worth another 1 mph?
The closer you get to 100% completion, the more effort it takes for even lesser gains, as you've already picked all the low-hanging fruit. Perfect is the enemy of done. And, in something totally subjective like art (which is what writing is), there is no singular "perfect" you can aim for.
Knowing when you are done is something YOU have to figure out yourself. And if you are a perfectionist, that would be incredibly hard to figure out.
