The fundamental attribution error refers to the tendency to attribute our own behavior to external (situational) factors while attributing others' behavior to internal (dispositional) factors. For example, if someone cuts us off in traffic, we might think they are rude, but if we cut someone off, we justify it by saying we were in a rush.
- Overestimating situational factors (A) is a description of the opposite of the fundamental attribution error, known as the actor-observer bias.
- Underestimating personal traits in social interactions (B) is not a clear explanation of the fundamental attribution error, as it does not directly relate to the attribution of others' behaviors.
- Assuming group behavior (D) is more related to groupthink or the assumption that group behaviors reflect individual intentions, but it is not the fundamental attribution error.
Therefore, the correct answer is (C).