I absolutley believe people have sadistic and masochistic sides.
Sadism, crushing your enemies, your competition, beating your potential mates into submission, that's just natural. All animals do it. As civilised creatures we have taboos against that sort of behavior, but we still do it in subtle or even unconscious ways.
Masochism is something we engage in because it makes us feel sexy. When someone says they just blew out their account trading, they are really saying "look at me, baby! I'm a big, sexy, risk taking, high-testosterone, badass"!
These are only primitive subconscious tendencies of course, but we can't keep the subconscious in check all the time.