Have you ever wondered what your personality says about you? I'm sure you know that you are either and extrovert or an introvert. Or that you are logical versus someone who feels then acts. So many characteristics that comprise who you are and yes, only 4 (four) letters define you in the world of science. Granted, science is always evolving so one's letters don't necessarily mean it's set in stone. They just define your dominant characteristics at a given time.