Psychologists believe this is a natural yet complex human reaction, which they call the bystander effect.
The bystander effect was first discovered in 1964 as a result of a very unfortunate event that happened outside Catherine Genovese's home in New York City. At three o'clock in the morning, someone attacked and murdered Genovese in front of her apartment building. But not one of those 38 witnesses did anything to help. No one reported the murder to the police.
Newspapers called the 38 witnesses selfish and uncaring, but social psychologists John Darley and Bibb Latane had a different theory. The reason they didn't help was not that they were uncaring or selfish people
Social psychologists believe the bystander effect can apply to a number of everyday situations. For example, on a busy sidewalk, you might not give money to a homeless man (or help someone who falls down)
Some cultures might put more importance on helping strangers than others do. Some cities and towns could be designed to be more friendly than others However, psychologists know that humans are naturally influenced by the presence of others around them even if they are not aware of it.