Everybody may have a devil inside them, but the people we term "psychopathic" or "sociopathic" are outliers on the bell curve of human behavior. Sociopaths have habits of exploitation, deceit, cheating, impulsiveness, manipulation, rationalization, and often of cruelty. Clever sociopaths are masters of disguise and of acting. There is a genetic component.
Clever sociopaths can put on a "mask of sanity" and, if careful enough, make successful lives in some careers.
When Your Child Is a Psychopath - The condition has long been considered untreatable. Experts can spot it in a child as young as 3 or 4.