humans are un predictable

It is surprising that when people see other people in pain, they do not stop to help them. I would assume that it is in our nature to help those who cannot help themselves. You always see a helping hand where ever you go. In the clip about the hit a run, no one comes to the injured person's aid. People just walk on by like he was invisible but in reality he was screaming for help. What kind of place do we live in if people don't help others?