In a complex and dynamic business world, effective leadership requires adaptability. Researchers have long recognized the importance of leader self-complexity in enhancing this adaptability. However, the underlying mechanisms by which leader self-complexity affects adaptability remain unclear. Furthermore, current theories and empirical studies on leader self-complexity mainly emphasize its advantages in facilitating leadership adaptability, while often overlooking potential costs. This research employs conservation of resources theory to uncover two distinct processes linking leader self-complexity to adaptability: a cognitive pathway (i.e., cognitive flexibility) and an affective pathway (i.e., role conflict and well-being), thereby exploring its dual effects. Data were collected from 330 US leaders at three time points. The results demonstrated that different components of leader self-complexity influenced adaptability via cognitive and affective pathways differently. The number of leadership roles did not show any significant positive or negative effect on adaptability through either pathway. Differentiation among roles increased role conflict and decreased well-being, which in turn negatively influenced cognitive flexibility and adaptability. Conversely, integration among roles showed positive effects on adaptability through both pathways.