["Human Resource Development Quarterly, EarlyView. ", "\nABSTRACT\nThis study extends Conservation of Resources (COR) theory by examining how perceived hierarchical threats experienced by supervisors cascade through dyadic relationships to shape subordinates' career self‐management. COR posits that resources are embedded within social passageways—relationships that enable or constrain their flow. Drawing on this logic, we conceptualize supervisor–subordinate dyads as resource passageways through which resource threats can cross over from one actor to another. Using time‐lagged, multi‐source data from 233 supervisor–subordinate dyads, we find that supervisors who feel their hierarchical position threatened engage in knowledge hiding as a resource‐conserving behavior, restricting subordinates' access to developmental resources. This defensive behavior produces a crossover effect: resource loss for supervisors triggers resource depletion for subordinates, prompting compensatory self‐management strategies. Specifically, subordinates high in status striving respond with careerist behaviors aimed at preserving external advancement resources, whereas those high in achievement striving adopt protean, self‐directed approaches to replenish internal resources. By extending COR beyond its traditional individual‐level application, this study illuminates how resource protection and loss spirals unfold relationally, offering a resource‐based explanation for divergent career orientations. The findings underscore the importance of HR systems and leadership development initiatives that mitigate hierarchical threat perceptions and sustain resource‐enabling passageways for employee growth.\n"]