It's not really a flaw in algorithms nor a skill in humans. It's (also?) a weakness in humans: someone mostly does X, we lean very strongly into the assumption

It's not really a flaw in algorithms nor a skill in humans. It's (also?) a weakness in humans: someone mostly does X, we lean very strongly into the assumption that they will never do !X. This is one of the most basic elements of human-to-human deceipt since ... well, since the dawn of any kind of recorded/remembered human history.