Community-Based Natural Resource Management (CBNRM) aims to resolve issues of legitimacy and social justice but in practice this aim is not always met. In this article, we contribute to the understanding of the outcomes of CBNRM by drawing on the concepts of governmentality, practice, and rationalities. We apply this conceptual approach to a CBNRM project in northern Tanzania: Enduimet Wildlife Management Area (WMA). Here a conflict emerged about proposed new livestock herding regulations which were intended to address a grass shortage affecting both wildlife and the Maasai community living in the WMA. Although these regulations were designed as part of the CBNRM process, they were resisted by community members. Our analysis highlights the role of conflicting rationalities between the WMA board and community members about the causes of and solutions to the grass shortage in the ensuing conflict. Specifically, we demonstrate how these conflicting rationalities can be understood as unintended outcomes of dynamic interactions between assumptions and intentions of involved actors, formal processes related to CBNRM, and the communication and participatory strategies employed around the introduction of the new livestock herding regulations. As such, our article illustrates the value of explicitly considering the role of practice in analysing unintended consequences of conservation interventions.