Objective: Embitterment encapsulates reactive emotions such as worthlessness or helplessness after negative life events that contravene one’s basic beliefs. However, no psychological model of the development of persistent embitterment has yet been investigated. We examined mediating factors for reactive embitterment, focusing on cognitive processes, including coping and rumination, among young South Korean adults. Method: A total of 1,000 young adults aged 18–35 answered an online survey questionnaire measuring distress caused by negative life events, coping strategies, rumination, and embitterment. To examine the mediating associations of coping and rumination with embitterment, we tested path analysis models separately. Results: Distress was both directly and indirectly related to embitterment (mediated by maladaptive strategies of dysfunctional coping and intrusive rumination; total association β = .54, p < .001). The estimated indirect association of distress via maladaptive strategy with embitterment was 0.45, accounting for 82.4% of the total association of distress on embitterment. The ratio of indirect association via maladaptive strategy to direct association was 4.64. The results of this study have implications for better clinical understanding and treatment of embitterment. Conclusions: The association between dysfunctional strategies and embitterment severity suggests that clinicians should attenuate potential aggravating factors, including dysfunctional coping and intrusive rumination. Given that a combination of dysfunctional coping approaches increased the risk of reactive embitterment fourfold, these variables can be regarded as important for the development of preventive service programs for people at risk of embitterment.