Zimbardo asserts that motives and needs that are generally positive can lead individuals astray when they are manipulated by social forces. The human need to belong, to be accepted by others, and for consistency between private attitudes and public behavior can pervert individuals’ thoughts, feelings, perceptions, and actions. Peer pressure is a strong social force, but “[t]here is no peer-pressure power without that push from self-pressure for Them to want You” (259). As British scholar C.S. Lewis explains, this pressure can impede initiative and hinder personal autonomy. The result is that social groups indirectly influence individuals to model the group’s behavior. Concurrently, self-serving biases distance individuals from this reality and make them vulnerable to prevent them from working to avoid this behavior “situational forces” (262).

Zimbardo explains several experiments that illustrate this premise. Firstly, he describes an experiment by social psychologist Muzafer Sherif, which placed subjects in a dark room with one stationary spotlight. The light appeared to move spontaneously, because in the dark room the subject has no frame of reference. Each subject was asked individually to judge the light’s movement, and the range described was wide. When Sherif then placed the individuals with other participants, each group created a standard range.