The effects of the similarity rule and the sufficiency rule in leader-member exchange (LMX) were tested through simulation. For this purpose, a model of leader-member exchange was proposed, and two personality traits—self-monitoring and reciprocity tendency—were considered. The results indicated that neither the similarity rule nor the sufficiency rule alone was adequate in explaining leader-member exchange. However, when both rules were applied simultaneously, significant results for leader-member exchange were obtained. Specifically, exchange occurred in dyads (leader-member) where the leader and member had similar self-monitoring tendencies and at least one person had a high reciprocity tendency. Conversely, exchange did not occur in dyads where the leader and member had different self-monitoring tendencies or where both had low reciprocity tendencies. In the discussion section, these results were examined from a leadership perspective, and personality traits and task characteristics that could influence leader-member exchange relationships were also discussed.