As soon as you convincingly argue that there is an underestimation, it goes away
It’s not a belief. It’s an entire cognitive profile that affects how they relate to and interact with other people, and the wrong beliefs are adaptive. For nice people, treating other people you know as nice-until-proven-evil opens up a much wider spectrum of cooperative interactions. For evil people, genuinely believing the people around you are just as self-interested gives you a bit more cover to be self-interested too.
It’s not a belief. It’s an entire cognitive profile that affects how they relate to and interact with other people, and the wrong beliefs are adaptive. For nice people, treating other people you know as nice-until-proven-evil opens up a much wider spectrum of cooperative interactions. For evil people, genuinely believing the people around you are just as self-interested gives you a bit more cover to be self-interested too.