Every single person I know well has a double standard for something. Such as “I don’t need to improve my driving but everyone else sure does” or a “do as I say not as I do” rule, etc. Though certainly some more than other. This leads me to believe all people do it in some way.
Is it simply human nature?
Read this in Subliminal by Leonard Mlodinow: human brains are biased towards optimism, but also, to value own decisions above others’. Baggage from thousands of years ago, but it’s there.