A bystander needs to recognize that something is wrong, assess the situation as an emergency or a scenario needing help, determine whether they feel personally responsible to act, decide on the best way to assist, and then take action. In this case, the couple walking down the stairs can clearly see that the man is completely immobilized.
Yet, they seem to have ignored the situation and continued on their way. What might be the reason for their lack of response? What would you do in such a situation? Now, take a look at the woman in the white jacket! At first, she briefly surveys the situation and chooses to walk away.