The interpersonal theory of suicide posits that failed interpersonal needs for efficacy and belongingness cause suicide ideation (Joiner, 2005). To distinguish whether their mechanism of action is interpersonal or via failure per se, an experimental paradigm was used. In Study 1 (n = 98), participants were randomly allocated to high or low perceived burdensomeness and thwarted belongingness conditions. Those who experienced high levels of the interpersonal factors expressed a heightened desire to disengage from the task. To test whether disengagement was caused by interpersonal factors or just poor performance, participants in Study 2 (n = 63) were randomly allocated to complete the task in collaborative (i.e., interpersonal) or competitive (i.e., intrapersonal) conditions. The deficits in persistence were greater among participants in the interpersonal condition, indicating that the interpersonal nature of perceived burdensomeness and thwarted belongingness makes these factors particularly pernicious, supporting the emphasis of the interpersonal theory of suicide.