Every economic model, no matter how detailed or how well designed, conceptually and empirically, is a vastly simplified representation of the world that we experience with all its intricacies on a day-to-day basis. Policymakers have needed to reach beyond models to broader - though less mathematically precise - hypotheses about how the world works.
A central bank needs to consider not only the most likely future path for the economy but also the distribution of possible outcomes around that path. The decisionmakers then need to reach a judgment about the probabilities, costs, and benefits of the various possible outcomes under alternative choices for policy.