The bystander effect is a social phenomenon where individuals are less likely to help a victim when other people are present. This occurs because people tend to assume that someone else will take action, leading to a diffusion of responsibility. As the number of bystanders increases, the likelihood of any one person intervening decreases. Research on the bystander effect was notably influenced by the case of Kitty Genovese, who was murdered in 1964 while numerous witnesses failed to assist her. This incident sparked studies in psychology, revealing that people often look to others for cues on how to behave in emergencies, which can result in inaction.