What psychological phenomenon describes the tendency to overestimate the commonality of one's opinions?

The phenomenon that describes the tendency to overestimate the commonality of one's opinions is known as false consensus effect. This cognitive bias occurs when individuals assume that their beliefs, values, and behaviors are shared by a larger number of people than they actually are. This effect can lead to an inflated sense of social validation for one's opinions, making individuals feel as though their perspectives are the norm.

Research has shown that people often project their own preferences and opinions onto others, leading to a distorted view of consensus. This can stem from social dynamics where individuals seek confirmation of their beliefs, thus reinforcing this overestimation. The false consensus effect plays a significant role in shaping interpersonal relationships, group behavior, and social interactions, as it influences how individuals engage with others who may or may not share their views.

The other options pertain to different concepts; the fundamental attribution error relates to how people interpret others' behaviors, frustration-aggression theory connects frustration with aggressive responses, and the mere-exposure effect deals with increased preference for stimuli that one has been exposed to repeatedly. None of these directly address the overestimation of how common one’s own opinions are among the population, reinforcing why the false consensus effect is the correct answer.