According to wikipedia; "The bystander effect, or bystanderapathy, is a social psychological phenomenon that refers to cases in which individuals do not offer any means of help to a victim when other people are present. The probability of help is inversely related to the number of bystanders."
Watching These People Suffer While People Just Walk By Is Distressing
This is an example of the bystander effect. The people walking in this video have several reasons not to help them man lying on the ground. The reasons range from giving excuses for his behavior ("he's drunk"), which to them is not a really important reason to help him, to putting the responsibility on others ("I'm sure someone else will handle it").