Recently, and for no apparent reason, a man gunned down a random college student in the middle of a crowded rail car in San Francisco.
You know what's even more unsettling?
There were no Good Samaritans. According to surveillance video, no one responded when the gunman drew his weapon. In fact, no one noticed at all. All of the passengers were so distracted by their smartphones that it took a gunshot to rouse them from their digital torpor.