Prior research shows that perceivers can judge some traits better than others in first impressions of targets. However, questions remain about which traits perceivers naturally do infer. Here, we develop an account of the "agreeableness asymmetry": although perceivers show little ability to accurately gauge target agreeableness in first impressions, we find that agreeableness is generally the most commonly-inferred disposition among the Big Five dimensions of personality (agreeableness, extraversion, conscientiousness, openness, and emotional stability). Using open-ended impressions based on photographs, videos, and face-to-face encounters, three studies show agreeableness as the most prevalently-judged of the Big Five although it is also poorly-judged in both absolute and relative terms. We use interpersonal power to reveal an underlying mechanism. Manipulating the power of perceivers relative to targets substantially shifts impression content, suggesting that habitual interaction and relational concerns may partially explain perceivers' chronic interest in assessing agreeableness despite their limited ability to do so.