When do you know you're at "The End"?

It's a question I have been asking myself a lot lately as I wrap up my first novel. This is the furthest I have ever made it in a work. I'm at the editing stage and I keep adding things, or thinking of different ways to phrase this and that. I wonder, is there such a thing as fine-tuning a piece of fiction to death? Yes, there probably is! I want to make it all flow together nicely, but I also don't want to be tedious.
So, my editing process involves a lot of highlighters. Different colors for different things. Mostly, I am searching for typos/grammatical errors, awkward phrasings and consistency.
Some days I think it's better than I remember and I am amazed I wrote it. Other days I am amazed I would actually consider letting other people read what I have written!
How will I know when it's finally done? I guess I'll just know.