I'm guilty of this even though I know better. I do this with several words, it's like some kind of deep seated whole-word dyslexia. I find those all the time when I proofread my stuff. I also do not know left from right. It all shows up after it's been submitted.
Errors show up best in print.
I blame it on being tired at the time, but I think I can get to a stage where I confuse myself, increasingly convinced that the rules are actually the opposite of correct. You want to try that when you're the navigator in a rally car. After entering the scenery at 130kmh once you never want to do it again. Never in a rally car, but it's been interesting behind the wheel on occasion. I get it wrong almost every time.