The present study aims to identify unrealistic career optimism among Korean high school students and to examine its characteristics. Cluster analysis was conducted to identify the number of groups classified by the reported levels of career aspirations and career preparation behaviors among 420 Korean high school students, and each group's characteristic was investigated using a series of one-way covariance (ANCOVA). Three clusters were identified: (a) Doer (30.3%), (b) Bystander (35%), and (c) Unrealistic Career Optimist (UCO; 34.7%). Clusters Doer and Bystander were characterized by high/low scores on both career aspirations and career preparation behaviors, respectively, while the cluster UCO endorsed high levels of career aspirations despite low levels of career preparation behaviors. Significant differences in optimism, subjective well-being, and career maturity between groups were documented, suggesting implications for both research and practice.