The bystander effect is a psychological tendency observed by psychologists. Essentially, it's been revealed that the likelihood of a person helping in an emergency decreases as the number of people nearby increases. For instance, someone witnessing a car crash who is walking alone at night would be more likely to intervene than a person amongst a crowd of 100 witnessing the same crash. This doesn't mean a victim is more likely to be helped if less people are around, however. The overall likelihood of a response may still be higher given the increased number of people.
Furthermore, the bystander effect should not be taken as an excuse for individuals failing to act. Any random individual still appears to be capable of doing the right thing, and specialized training can improve the frequency with which someone will respond. Awareness of the bystander effect can enable someone to reflect on it in their own life to ensure they do not allow victims of tragedy to go unaided. For instance, a famous case involved a women named Kitty Genovese. Her death is responsible for the coining of the term "bystander effect."
More specifically, she was a victim of a stabbing in New York. After the tragedy, it was revealed that over thirty people were in the area and among those who heard her scream, most assumed it was nothing serious. They did not bother to inquire further and ensure that the women did not need help. A famous finale of the television program Seinfeld has a humorous take on the rather tragic bystander effect, but the real life consequences are far from humorous.
Not only has the bystander effect occurred in response to murders, but it has also been present in cases of rape. In 2009, a fifteen year old girl was gang-raped and violently assaulted while twenty high-school students stood by doing nothing. This occurred over a two hour period. Another famous occurrence of the bystander effect would be in the actions of Nazi Germany and its soldiers. Many individuals failed to speak out against atrocities even before the fascist regime was fully established in its power.
Some may point to the bystander effect as an example of the human tendency to be subordinate to stronger figures and conform to the behavior of others. Once a few people are doing nothing, it seems like the reasonable thing to do. Much of human behavior and moral decency is taught and enforced. Part of being an ethical human being should involve reflection on our own morals and personal flaws - this is necessary to avoid such tragic results as seen in cases of the bystander effect.