Bystander Effect

The Bystander Effect is a phenomenon by which observers of an emergency situation are less likely to offer assistance to a victim when others are present. The relationship between the number of observers and the likelihood of aid being offered are directly inverse, where the greater the crowd, the less likely someone is to stop and render aid.

Social psychologists believe that the phenomena is tied to three main processes: noticing, interpretation, and taking responsibility. Noticing is often impacted by cultural conditioning. Western society holds that staring is rude, so in social situations, individuals are far more likely to keep their attention to themselves, which may prevent them from noticing the problem in the first place. Once the situation has succeeded in catching a bystanders notice, they then must interpret the situation as requiring intervention. In large crowds, individuals often take clues from the actions of others, so if no one is acting, the individual is far less likely to buck the trend and intervene (which can be a seen as conformity via social proof). The final hurdle is that in larger groups, individuals are far more likely to believe that someone else will handle the problem, which often means that no one is willing to step in and take responsibility.

Unfortunately, this can lead to things like this happening:

Here, it is a set up and no one is actually harmed, but in one famous case, Kitty Genovese was stabbed and left for dead while more than 20 people just watched. Some Social Psychologists cite this story as being grossly inflated as to the effect of the bystander effect, but in a more recent case, a homeless man was stabbed after coming to the aid of a woman being mugged. In his case, people walked over and around him as he died (one even took pictures) but no one stopped to offer any aid.