<p>Self-concept plays a pivotal role in self-control. However, empirical research has not yet fully explored how self-concept clarity affects self-control. We hypothesized that self-concept clarity influences self-control through rumination. Five studies (<i>N</i> = 895) have consistently supported our mediation mechanism. Low self-concept clarity was positively related to rumination and negatively associated with self-control (Study 1). In situations that prompt self-knowledge conflict, individuals with low trait self-concept clarity reported heightened levels of rumination (Study 2). Inducing rumination resulted in diminished self-control and increased impulsivity (Study 3). The manipulation of individual self-concept clarity could lead to increased rumination and decreased self-control (Study 4). Even with the introduction of new manipulation methods and self-esteem control, rumination continues to mediate the impact of self-concept clarity on self-control (Study 5). Overall, these findings underscore the critical role of self-concept clarity in developing self-control and contribute to our understanding of the underlying mechanisms of self-control. Additionally, these results provide an empirical foundation for interventions aimed at mitigating adverse outcomes resulting from failures in self-control.</p>