There are many stages involved in writing a book, from the early minutes/hours/days when an idea starts to emerge until the day the first copy is in my hands: the research, the writing of several drafts, the comments of the editor, followed by more rewriting and more comments and more tweaking, and finally the sense that I've told my story as well as I can. A time to relax a little, clean out my files, sew on buttons, answer letters.
But not so fast! You're not done yet! The copy editor has yet to speak. This person not only looks for sloppy punctuation and points out that you have used "get" or "got" a few dozen times too many and notices that the guy you call Sam on page 37 suddenly becomes Bill on page 119. The CE, as she's known, also acts as a fact-checker (sometimes another person takes over this job). If one of your characters plays a song on the piano, was that song actually written by that time? If you write that 1920s movie star Rudolph Valentino died on Monday August 23rd, why does your character, a devoted Valentino fan, not hear about it on the radio until Wednesday the 25th?
It has to be said: Copy editors are a pain in the neck, but they also save your neck, too. Because if those little errors and inconsistencies and quirks aren't caught now, you can be sure they will be later. Years ago I mentioned a "horny toad" in Texas and how it hopped, and I was promptly nailed by a gleeful expert who pointed out that they are not toads but lizards, they don't hop, and since I was so wrong about that fact he would never again trust anything I wrote.
And that's why I say thank you to Lisa and all the other unsung copy editors who have kept me from embarrassing errors in so many books over so many years.