In nature, the psychopath feels no pain beyond his own, an island unto himself in an emotional wasteland.

As many as one percent of people — and nearly one in every four inmates in American prisons — may exhibit traits consistent with the personality disorder of psychopathy: a lack of empathy and remorse, shallow affect, glibness, manipulation, and callousness. Under the lens of modern brain scanning technology in a study of U.S. prisoners, people with psychopathy to varying degrees not only fail to experience empathy for another’s pain, but also derive pleasure from the thought.

via Psychopaths Feel No Empathy For Others; How Do Their Brains Differ?.