Research on knowledge hiding, the intentional attempt to withhold knowledge that others have requested, strikingly shows its detrimental consequences. But, if it has only negative effects, why do employees hide knowledge in their everyday work at all? With this diary study, we address this question, shedding light on the instrumentality of knowledge hiding. Specifically, placing it within the transactional stress model, we argue that deceptive knowledge hiding (playing dumb and evasive hiding) may function as coping, relating negatively to psychological strain responses to experienced interpersonal conflict. Accordingly, we tested evasive hiding and playing dumb as mediators of the day-specific relationship between conflict and end-of-work exhaustion and negative affect. Based on data of 101 employees who reported on 615 workdays, results of multilevel path analyses showed relationship conflict positively related to evasive hiding and playing dumb. Playing dumb was negatively related to end-of-work psychological strain responses, resulting in inconsistent mediation. Evasive hiding was unrelated to psychological strain. Showing the potential intrapersonal benefits of playing dumb, this article helps to better understand the occurrence of enacted ‘negative’ interpersonal work behaviors, yielding important implications for research and practice.