I have two small children, and it seems like there’s a certain age where they decide that how things usually are is how they should be. How they must be!
I feel like a classic example for this is “Boys don’t have long hair!”
And while I think kids are known for doing this because they do it clumsily, I think adults do it as well. It seems like a lot of social changes over the past several decades (past century?) are from people pushing back against the expectation that how most people do something is how it should be done. The only acceptable way!
This is a big part of how I frame “Social Justice” issues for my kids. I don’t think “there are bad people out there who treat people badly just because of X” is actually a helpful way of thinking about it. If I have to keep it simple so that it can fit in my kids’ minds, I want to keep it in line with how I see the world, too: “a common mistake people make is thinking that the way things usually are, or the way they always see things done, is the way things should be done. Mama and I believe that it’s okay for people to be different, and that they shouldn’t be forced to hide it.”
I’m sure this is already described somewhere in the Wikipedia List of Cognitive Biases, but there’s an awful lot of things on that list and five minutes skimming it didn’t turn up a matching concept.