I'm reminded of some popular news reporting of a psychological study (who knows whether it's reproducible), something like... People who behaved in some specific dishonest way also thought other people tended to have a similar level of honesty to themselves. Compared to people who didn't behave in that dishonest way, and who thought others tended to have a similar level of honesty to themselves.

How the causality works there, I don't have good guesses.

But the supposed phenomenon could reduce to simply differing conceptions of what the real world is.