It has to be that. It can't be carelessness or anything that would be the writer's fault. Right?
The hard truth is that, as stated perfectly in a Facebook meme, "I do my best proofreading after I hit 'send'." I know that I do my very best to find all the typos, glitches, misspelled words, missing words, and messed-up indentations and paragraph breaks BEFORE I send my work to my beta-readers, editors, and--especially--my publisher. Imagine my chagrin when my manuscript comes back to me with a list of things that need to be corrected attached. And it's not a short list, either.
So I spend the next few days going over the manuscript line by line, scrupulously fixing all the mistakes that were brought to my attention. And once done, I send it off again.
And I get it back a few days later. With a new list of new mistakes.
It's harder this time around. I've already seen the manuscript at least a dozen times already, so I have several key passages memorized. That's where the gremlins hide; in plain sight in the most often read paragraphs. Because the writer KNOWS what the paragraph is supposed to say, so the eyes and brain skip over the exact words on the page, including the word "her" masquerading as "he", the character's name being substituted for another's, and an errant comma popping up where it doesn't belong.
This is where a writer needs to be patient, not just with the extra eyes that spot all of the gremlins' shenanigans, but with him or herself. It's tempting, after two or three rounds of corrections with a deadline looming, to just say, "Okay, the corrections are done, just go with it!" I've hit that wall more than once, especially with this last book that I've been working on. But it's important to soldier on and not be discouraged. It helps to remind oneself that it's the writer who will look foolish when the reading public finds the errors.
I've learned to be patient and not rush through the editing process, no matter how badly I want to be done and move on to publication. I want to make a good impression on the readers so that they will want to read more of my work. Errors will still sneak through (those gremlins have an uncanny knack for being persistent!) but a large amount of mistakes send a message to the reader that the author doesn't care enough to deliver the best work they can. That's definitely not the message I want to send my readers.
They deserve my very best!
Getting after the gremlins... caffeine helps!