When you finish your manuscript, because you've been working so closely on it for so long, you've probably become kind of blind to the errors that still exist in it. You know, like when your beard has started to grow in gray, but you don't really see it.
But, as you force yourself to look a little more closely, you realize that some of your comedy falls flat, the transitions seem rough, and there's a chance that you changed a character's name in chapter 23, and - worst of all - you were typing so fast that you left major typos throughout. Basically, you realize that the highlights that you thought were so great are actually gray hairs.
So you run spell check - and maybe even a grammar check - and you think you've probably caught most of the really egregious stuff. Unfortunately, because most of these programs aim for about eighth-grade level language usage, although you've "fixed" a lot of "errors" you end up with a nice, kind of all-one-tone, manuscript. This is also how it looks when you first do a really heavy application of dye - you get an all-one-tone beard.
Okay. Sure. From the front (or at a distance) it might look fine. The major errors have been tackled. The typos seem to all be gone. But, since your "editor" was a machine without an ear for style or tone, you might have a few issues when you look closer.
Possibly a section where a character named "Sandy" has all become lower case "sandy" because the spell check changed it.
Or maybe a section where the "heir" to the throne has become the "hair" to the throne - which the program won't notice, because the spelling is correct. Or a section where the little brush you were using seemed to miss the patch just beyond your mustache/goatee area and has left the gray intact.
So, having run the programs, you're left with something which might look fake from the front - and not really "you" - and up close probably still have errors. What can you do? First of all, talk to an actual editor, who will work with you to bring out the "you" in your manuscript.
Okay. Yes. It's going to look kind of weird for a while as you work on it. You're probably going to have Track Changes all over the place, and additions and deletions that make it hard to read. (Or, in the case of beard dyeing, you end up with goop all over your face, making it look like you just did a headlong dive into some kind of jelly.)
You're most likely going to end up swearing at your computer and any other tool you've been using thinking that it's never going to be right and wishing you'd just left it alone from the outset - or never written it (or grown it) in the first place.
You're not only ready to throw in the towel, you're ready to pitch the entire thing and give up.
But then you start talking to your editor and looking at what the two of you have done. You start seeing that it's beginning to look... well... not exactly the way you wanted it to look, but closer. You're beginning to see more of yourself in it.
Of course, until you and your editor can reach a really good balance, you might find yourself having a read-through where you find that you're all back to one tone, again. That you've lost yourself and that there's no highlights or lowlights. Everything has gone flat and you think "Oh, crap, back to square one (or maybe square three)."
But, as with any good relationship, working with an editor takes time. So as you work together and as you spend time with the manuscript - alone or with your editor or beta readers - you can finally take a long look at what's going on. You can decide that some characters probably don't have perfect grammar - but that your narration might still need to be proper. You can let your editor tell you that readers will appreciate sentences that read like sentences, and not just groups of adjectives. You can decide whether the "rule" that there should be no "to be" verbs is right for you. (Sidenote: that "rule" really only works for about 5% of authors.)
And, with time and a little growth - both for you and the manuscript - you might find that the book feels more like "you" - an enhanced version of you, if your editor is good at his/her job. You might find that the "absolutely perfect" version isn't right for you. That a few stray gray hairs make it more natural, and that you - and your readers - actually prefer the highlights and lowlights more than the all-one-color manuscript you almost gave them.
And, if not, you can always head back to step one - maybe with a new editorial color in mind.