Perfectionism, a focused self-concept, and erroneous beliefs have been implicated in the development and maintenance of various disordered behaviors. However, researchers have yet to examine how these factors combine to explain different disordered behaviors. Herein, we addressed this gap and hypothesized a moderated-mediation model whereby perfectionism fosters the development of disordered behaviors through a focused self-concept. Critically, the effect of a focused self-concept on disordered behaviors is specific to people with erroneous beliefs about their disordered behaviors. The model was tested in the contexts of disordered gambling and disordered eating, particularly dietary restraint.