A popular theory is that something goes wrong with the empathy circuits in the brain of the cruel person. And that’s when you get violent or abusive behavior toward other people. This phenomenon is often described as
empathy erosion. There may be many different causes of empathy erosion, and it could be a temporary state or a general tendency, depending on the person and their circumstances. But when empathy erosion occurs, it translates into a failure to see another person as fully human. And when we don’t see other people as fully human, it’s much easier for us to treat them cruelly.