Psychology is the science of behavior and mental processes. Mass can be interpreted as a form of collectivism (togetherness). Therefore the psychology of the mass will relate the behavior carried out jointly by a group of masses. This phenomenon of togetherness is also termed as Collective Behavior (Collective Behavior)

In collective behavior, a person or group of people wants to make a social change in their group, its institutions, the community. These group actions are organized, and there are also unorganized actions. This organized action is then widely known as the social movement (Social Movement).

Collective behavior in the form of social movements, often arise when in social interactions that occur unstructured situation, ambigious (coercion / confusing), and unstable.

Reicher & Potter (1985) identifies the five basic types of errors in the psychology of the crowd (mass behavior) in the past and the present. These include: (1) the abstraction of the crowded episodes from inter-group conflict, (2) the failure to explain the dynamic process, (3) the excessive anonymity of its membership, (4) the failure to understand the motives of the members of the crowd, and (5) always emphasize the negative aspects of the crowd.

Reicher (1987), Reicher & Potter (1985) has seen the existence of two (2) forms of bias in view of crowds theory that is political bias and perspective bias. Political bias occurs because the crowd theory is structured as an attempt to maintain the social order of mobs and the action of the crowd is always seen as a social conflict. Meanwhile, perspective bias occurs because experts only act as outsiders who only observe the problem. As a result, there was a mistake in viewing the crowd's action objectively.

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