Future leaders will have the challenging task of transitioning current societal practices and organizations towards sustainability, but we lack in-depth characterizations of young sustainability leadership students within specialized higher education programs. Understanding their aspirations, doubts and fears may help educators to provide tailored and innovative teaching. In this study, we engage 24 students of a Finnish sustainability leadership Master's degree program through a workshop, a survey, and interviews with the aim of understanding how they conceptualize and operationalize sustainability. A thematic analysis indicates that their understanding is contested--they feel responsibility, but they channel it primarily through individual action and often value moderation (i.e. not taking action to perceived extremes); engaging the public is seen as important, but some suspect that human selfishness cannot be changed; and post-capitalist views exist alongside advocacy for business-as-usual consumption-based happiness. Based on these insights, we outline implications for research and education.