Michael Stone claims to understand the human psyche. He has developed his very own method for judging the personality of people. For this test he has made a list of hundreds of personality traits. By defining all the different traits and making a comparison to other lists and diagrams, he can with certainty tell who is a psychopath, sociopath, murderer and so on. Errol Morris talks to Michael Stone in an attempt to find out who he is. Has he lost himself in the quest to understand others?

• Errol Morris