It has been shown that people tend to view opponents as biased. Recent theoretical studies showed that this tendency occurs due to naïve realism. People tend to be overconfident about their objectivity ─ they believe they see the world as it really is (Naïve realism: Ross & Ward, 1995) ─ hence, they assume that people who have a different view must be biased (Pronin et al., 2004). This study examines the effect of encountering clear demonstrations that personal sensory perceptions are not necessarily accurate on the perception of opponents’ bias in their social judgment through exposure to visual illusions. A total of 87 participants were grouped by whether or not they experienced visual illusions. Participants who experienced visual illusions rated opponents as having fewer biases in their social judgments than participants who did not experience visual illusions. This suggested that a person’s overconfidence in their own perception ─ “I see the world as it really is” ─ might be one of the causes of people’s negative perception of opponents.