It is a funny fact about human behavior. Whenever there is someone in immediate peril and urgent rescue by even a single person means the difference between life and death, the chances whether the rescue is offered depends mainly on the number of people witnessing the scence. The chances vary inversely with the size of the crowd. If there is only one single person, it is much more likely that he or she would step forward to help. The chances get slimmer when there are more people say two, three, four or more.