In response to the increasing recognition of the need for sustainable food systems, research on students' and educators' knowledge of food systems and sustainability more broadly has grown but has generally focused on what people "fail" to understand. Moving away from this deficit approach, the present study used semi-structured interviews to explore how 12 pre-service teachers (PSTs) in the US consider sustainability in terms of the trade-offs--or concurrent costs and benefits--associated with using different agricultural resources over short, medium, and long terms. Drawing upon the constructs of framing, metacognition, and complex causality, the study found that the majority of PSTs referred to indirect experiences of seeing or hearing about agricultural resources to demonstrate stable knowledge of short-term trade-offs and construct tentative knowledge about medium-term trade-offs. Few described long-term trade-offs. Most participants also acknowledged some gaps in their knowledge in discussing trade-offs across the different time scales. Findings suggest the importance of leveraging and building upon educators' (and ultimately students') prior experiences to build their understanding of complex trade-offs that underlie food systems. The study also illustrates the value of using the concept of trade-offs across time scales to explore people's conceptions and understandings of sustainability.