So far, the dominant understanding of psychopathy was that they basically lack emotions such as fear or distress. If you clap your hands behind someone’s back, she will startle, and you can measure how her palms get sweaty. If you do that with individuals with psychopathy, experiments have shown that their response is flattened. They barely startle and their hands stay dry. Now imagine, if you had never felt real fear or distress, how could you empathize with the fear or distress of others?