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?
Oi boy!
The very short answer is: yes. Usually it’s called psychological biases and literally everyone has them - even people who are studying them daily, to be very clear. They just become way more self aware.
The reason is simple: our brains are gooey, bad calculators - but awesome pattern recognizers. Even if there are no patterns.
This leads to things we observe to be “clear” to us - but our own behavior needs a lot of mental effort to be observed by one self.
Just think about a normal dialogue and try to think about your body language, tone of voice, body odor, social appearance and all the other micro information you’re sending out - while talking.
It’s less about a double standard and more about what we evaluate about ourselves ehwne not investing additional effort.