(CNN) 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.

There was a twist: Before the students left to give their lecture, some were told they were late. Others weren’t told anything at all. That little variation in their situation made all the difference in their behavior.

Only 10% of the students who were “late” stopped to help the slumping man, whereas nearly two-thirds of those who were “on time” stopped to offer help. As the psychologists put it, “On several occasions, a seminary student going to give his talk on the parable of the Good Samaritan literally stepped over the victim as he hurried on his way.”

The two psychologists didn’t know it then — and it certainly wasn’t their intent — but through their study, they demonstrated something unexpected: a key driver of gun violence in America.  Read More