Social psychologists study how social roles, attitudes, relationships, and groups influence individuals; cultural psychologists study the influence of culture on human behavior. Many cultural rules, such as those governing correct conversational distance, are unspoken but nonetheless powerful.

Milgram's obedience study illustrates the power of norms and roles to affect individual actions; most people in the role of “teacher” inflicted what they thought was extreme shock on another person because of the authority of the experimenter.

Similarly, in the Stanford prison study, college students tended to behave in accordance with the role of “prisoner” or “guard” that they had been assigned. The social situation exerted a powerful influence on individuals' behavior, often prompting them to behavior in uncharacteristic ways.

Obedience to authority contributes to the smooth running of society, but obedience can also lead to actions that are deadly, foolish, or illegal. People obey orders because they can be punished if they do not, out of respect for authority, and to gain advantages. Even when they would rather not obey, they may do so because they have been entrapped, justifying each step and decision they make, and handing over responsibility for any harmful actions they commit to the authority.

According to attribution theory, people are motivated to search for causes to which they can attribute their own and other people's behavior. Their attributions may be situational or dispositional. The fundamental attribution error occurs when people overestimate personality traits as a cause of behavior and underestimate the influence of the situation. Attributions are further influenced by three self-serving biases: the bias to choose the most flattering and forgiving explanations of our own behavior; the bias that we are better, smarter, and kinder than others; and the bias that the world is fair (the just-world hypothesis).

People hold many attitudes about people, things, and ideas. Attitudes may be explicit (conscious) or implicit (unconscious). Attitudes may change through experience, conscious decision, or as an effort to reduce cognitive dissonance. One powerful way to influence attitudes is by taking advantage of the familiarity effect and the validity effect: Simply exposing people repeatedly to a name or product makes them like it more, and repeating a statement over and over again makes it seem more believable.

Suicide bombers and terrorists have not been “brainwashed” and most are not psychopaths or mentally ill. They have been entrapped into taking increasingly violent actions against real and perceived enemies; encouraged to attribute all problems to that one enemy; offered a new identity and salvation; and cut off from access to dissonant information.

In groups, individuals often behave differently than they would on their own. Conformity permits the smooth running of society and allows people to feel in harmony with others like them. Two basic, beneficial motives for conformity are the need for social acceptance and the need for information. But as the Asch experiment showed, most people will conform to the judgments of others even when the others are obviously wrong.

Close-knit groups are vulnerable to groupthink, the tendency of group members to think alike, censor themselves, actively suppress disagreement, and feel that their decisions are invulnerable. Groupthink often produces faulty decisions because group members fail to seek disconfirming evidence for their ideas. However, groups can be structured to counteract groupthink.

Sometimes a group's collective judgment is better than that of its individual members—the “wisdom of crowds.” But crowds can also spread panic, rumor, and misinformation. Diffusion of responsibili/ty in a group can lead to inaction on the part of individuals, as in bystander apathy. The diffusion of responsibility is likely to occur under conditions that promote deindividuation, the loss of awareness of one's individuality.

In some situations, crowd norms lead deindividuated people to behave aggressively, but in others, crowd norms foster helpfulness. In truly dangerous, unambiguous emergencies people are more likely to help, and in fact are often spurred to do so by the presence of others. The willingness to speak up for an unpopular opinion, blow the whistle on illegal practices, or help a stranger in trouble and perform other acts of altruism is partly a matter of personal belief and conscience. But several situational factors are also important: The person perceives that help is needed; cultural norms support taking action; the person has an ally; and the person becomes entrapped in a commitment to help or dissent.

People develop social identities based on their ethnicity, including nationality, religion, occupation, and other social memberships. In culturally diverse societies, many people face the problem of balancing their ethnic identity with acculturation into the larger society.

Ethnocentrism, the belief that one's own ethnic group or religion is superior to all others, promotes “us–them” thinking. One effective strategy for reducing us–them thinking and hostility between groups is interdependence, having both sides work together to reach a common goal.

Stereotypes help people rapidly process new information, organize experience, and predict how others will behave. But they distort reality by exaggerating differences between groups, underestimating the differences within groups, and producing selective perception.

A prejudice is an unreasonable negative feeling toward a category of people. Psychologically, prejudice wards off feelings of anxiety and doubt and bolsters self-esteem when a person feels threatened (by providing a scapegoat). Prejudice also has social causes: People acquire prejudices mindlessly, through conformity and parental lessons. Prejudice also serves to justify a majority group's economic interests and dominance. Finally, prejudice serves the cultural and national purpose of bonding people to their social groups and nations, and in extreme cases justifying war.

Psychologists disagree on whether racism and other prejudices are declining or have merely taken new forms. Some are trying to measure prejudice indirectly, by measuring social distance and instances of “microaggressions”; measuring unequal treatment by the police or other institutions; seeing whether people are more likely to behave aggressively toward a target when they are stressed or angry; observing changes in the brain; or assessing unconscious positive or negative associations with a group, as with the Implicit Association Test(IAT). However, the IAT has many critics who claim it is not capturing true prejudice.

Efforts to reduce prejudice need to target both the explicit and implicit attitudes that people have. Four conditions help to reduce two groups' mutual prejudices and conflicts: Both sides must have equal legal status, economic standing, and power; both sides must have the legal, moral, and economic support of authorities and cultural institutions; both sides must have opportunities to work and socialize together informally and formally (the contact hypothesis); and both sides must work together for a common goal.

Although many people believe that only bad people do bad deeds, the principles of social and cultural psychology show that under certain conditions, good people often can be induced to do bad things too. Everyone is influenced to one degree or another by the social processes of obedience, entrapment, conformity, persuasion, bystander apathy, groupthink, deindividuation, ethnocentrism, stereotyping, and prejudice.