Are you talking about people who are sadistic w/ consensual partners, or people who are sadistic just because? People who are just sadistic are generally sociopathic, meaning they can't feel empathy or other emotions outside or anger. They inflict pain on others in order to feel something, to exercise god-like controls or to experience strong emotions vicariously through their victims.
Yes. The source originated most likely from an even that happened before the age of 5. They have a fixation.
i would say frustration may have something to do with me being sadistic,but i'm not sure i have been that way all my life.i try to control it,but its always there.
agree with fascade