In 1973, two psychologists came up with a clever experiment. They took a group of Princeton Theological Seminary students and asked them to walk across campus to give a lecture on the parable of the “Good Samaritan.” Along their route, the psychologists positioned someone in a doorway, not moving, eyes closed, coughing and groaning as the study subjects went by — someone, in other words, clearly in need of a Good Samaritan’s help.