Change Blindness is a real thing. I wouldn't copy/paste Grace's explanation onto a test answer or anything, but it happens. And I don't mean "I read it in a book, so I assume it's real" happens, I mean "I have experienced it first hand and seen it mess with other people" real.
A particularly awkward example, and one of the reasons I brought up haircuts, was one time when someone I knew shaved their mustache and both myself and one other person couldn't realize they had done so to save our lives. They even said "notice anything different" and we were BAFFLED. When they finally pointed out that they had shaved their mustache, it seemed like some sort of wizardry.
Heck, maybe it was. It's basically been confirmed that there's a link between wizards and facial hair.