This article extends mixed-methods longitudinal research with school and district leaders (2008-present) about their most pressing leadership challenges. Here--through in-depth, qualitative interviews--we explore how a subsample of 30 principals described and understood their "internal experiences" of addressing pressing challenges. More specifically, using an adaptive/technical lens, social-emotional frameworks, and constructive-developmental theory, we illuminate how principals' social-emotional and developmental capacities influenced their leadership, and highlight findings with in-depth mini-cases. By focusing on the inner workings of principals' leadership for managing change, this article offers implications for professional practice and school-wide change locally and globally, leadership preparation, policy, and future research.