Thank god for copy editors. Editors basically work to make a story better, and to prevent the authors from looking like idiots. The main editor mostly works on big picture stuff, helping the novel be the best it can be. Copy editors, meanwhile, work on the tiny little details. They fix grammar and punctuation, standarize spelling and capitalization and word-use to the "house style," and, perhaps most importantly, are absolute geniuses who catch the author's little contradictions that got lost in 100,000 words of fantasy narrative.
Seriously. Geniuses. Like "on page three you said the building had one tower, but here on page 303 you say towers -- which is it?" level super-brains. They're the people who notice that you said something happened three days ago, but the characters have only slept twice. They catch that your character had blue eyes in most of the novel, but grey eyes in this one scene. They are fantastic at pulling out logical inconsistencies in the novel, the brain-hiccups that come up when you spend hundreds of hours revising and refining a story and forget to account for certain changes all the way through.
Unfortunately, this can mean that reviewing your copy edits leads to pulling-out-your-hair frustration. It's a bit embarrassing to see that you mixed up "further" and "farther" for the 500th time (sorry, wonderful copy editor!). But when they bring up a logical flaw that should have been obvious, but somehow you missed on the five million times you read the book, and now you have about a week to fix it? Eeek.
But at least the copy editor found it for you before the book went to print. They are indispensable, magical beings.
Copy editing also makes me realize that, no matter how much I think I understand the differences between British English and American English, I never really know all the differences. For example, America, why don't you say "dreamt" instead of "dreamed"? That "t" is really nice, I promise. It adds a satisfying little click to the end of the word. And wouldn't you rather move towards something instead of just toward it? What did the letter s ever do to you?
I write in "American English" these days, after four years at an American college, and three years with an American publisher, but... I don't, really. I write a horrifying hybrid of British and American, where 'z's spring to my fingers and 'u's get lost somewhere along the way, but which still makes my American copy editor scream in frustration because dammit, forward doesn't need an s at the end!
As I write this, I have two more days left to review my copy edits and work on fixing these problems. Two more days, and then the novel gets locked down. This becomes the version that is printed for review copies. It becomes hard to make changes that aren't on a typo-level. Scary stuff. But less scary with a genius copy editor on my side!