In this article, I argue that much of the discourse observable within the UN constitutes neither unnecessary and unproductive ‘talk’ nor efforts to convince outside audiences of its legitimacy, but actually a form of institutional self-legitimation that is key to its ability to function. Using the case of the UN's Department of Peacekeeping Operations (DPKO), I show that because the organisation has a multifaceted organisational identity, it faces situations where it is forced to choose between multiple but equally appropriate courses of action, and it uses self-legitimation alongside other mechanisms to overcome these tensions. I specify three sets of circumstances in which this occurs, showing how DPKO uses discourse that simplifies and exceptionalises in a bid to reconcile or downplay these contradictions and reassert a cohesive and legitimate organisational identity internally. This simplification and exceptionalisation in turn serve an enabling function, allowing DPKO to continue operating in conditions of complexity by decreasing risk aversion and instilling a deep sense of professional loyalty in staff. At the same time, such discursive processes are costly and may entrench inefficient practices, rendering the effects of self-legitimising discourse paradoxical: they may enable action, but they reduce the efficiency and effectiveness of that action.