De-individuation is a social psychological explanation for aggression. De-individuation theory was first introduced by Zimbardo (1969), who suggested that de-individuation occurs when people who are part of a relatively anonymous group, lose their personal identity and consequently their inhibitions in relation to violence. According to Diener (1980), deindividuation occurs as a result of four factors: 1) poor self-monitoring of behaviour; 2) reduced need for social approval; 3) reduced inhibitions against behaving impulsively; and 4) reduced rational thinking.