International Relations scholars have long debated whether the American public is allergic to realism, which raises the question of how they would “contract” it in the first place. We argue that realism isn’t just an IR paradigm, but a belief system, whose relationship with other ideological systems in public opinion has rarely been fully examined. Operationalizing this disposition in ordinary citizens as “folk realism,” we investigate its relationship with a variety of personality traits, foreign policy orientations, and political knowledge. We then present the results of a laboratory experiment probing psychological microfoundations for realist theory, manipulating the amount of information subjects have about a foreign policy conflict to determine whether uncertainty leads individuals to adopt more realist views, and whether realists and idealists respond to uncertainty and fear differently. We find that many of realism’s causal mechanisms are conditional on whether subjects already hold realist views, and suggest that emotions like fear may play a larger role in realist theory than many realists have assumed.