Invitation to Psychology, Fourth Edition defines fundamental attribution error as "The tendency, in explaining other people's behavior, to overestimate personality factors and underestimate the influence of the situation" (338). More simply, the fundamental attribution error does not take into account the situational factors of an experiment but focuses on the preexisting behaviors of those involved to find an explanation for a certain outcome. For example, the students involved with the Stanford Prison Experiment were told to act as prisoners and guards. Though the events got out of hand, it is not fair to assume that the guards were predisposed to violence, that the prisoners were weak and cowardly. They were asked to act a certain way, and though the behavior escalated, it can not be attributed to their behaviors in everyday life.
The easiest attribution to make is classified as dispositional, meaning a person attributes some behaviors based on a person's usual inclination. A person acts a certain way, that may even be different from their normal behavior, because he or she has always had a trait or quality that makes them act they way they do. Therefore, others do not take a leap into 'whys' but remain grounded with what they know.
Interestingly, this error is prevalent in Western cultures moreso than Eastern. Invitation to Psychology cites "In countries such as India, where everyone is embedded in caste and family networks, and Japan, China, Korea, and Hong Kong, where people are more group oriented than in the West, people are more likely to be aware of situational constraints on behavior" (338). This means that is a person were to change their normal behavior, a family member or friend or even a co-worker is likely to notice and also more likely to assume a situational factor os behind the change rather than a dispositional one.