The authors tested the role of dispositions and self-regulatory mechanisms in the relation between social exclusion and self-defeating behavior. The authors manipulated the perception of social exclusion by giving participants feedback about the likelihood of their ending up alone. The authors randomly assigned participants to the following experimental conditions that varied by type of feedback: (a) social inclusion (n = 31), (b) social exclusion (n = 32), and (c) control (n = 30). Before receiving the feedback, each participant completed a questionnaire about his or her personality. Both before and after receiving the feedback, each participant also completed a questionnaire about self-regulatory variables. Participants then performed a task concerning a type of self-defeating behavior: misguided persistence. Results suggest that to avoid problems of adaptation, it is wise for psychologists to promote social self-efficacy, incremental implicit theories of ability, and positive emotion in groups threatened with social exclusion.