. Mean dynamics describe the convergence to self-confirming equilibria of selfreferential systems under discounted least squares learning. Escape dynamics recurrently propel away from a self-confirming equilibrium. In a model with a unique self-confirming equilibrium, the escape dynamics make the government discover too strong a version of the natural rate hypothesis. The escape route dynamics cause recurrent outcomes close to the Ramsey (commitment) inflation rate in a model with an adaptive government. Key Words: Self-confirming equilibrium, mean dynamics, escape route, large deviation, natural rate of unemployment, adaptation, experimentation trap. `If an unlikely event occurs, it is very likely to occur in the most likely way.' Michael Harrison 1. INTRODUCTION Building on work by Sims (1988) and Chung (1990), Sargent (1999) showed how a government adaptively fitting an approximating Phillips curve model recurrently sets inflation near the optimal time-inconsistent ouctome, althoug...

A decision maker doubts the stationarity of his environment. In response, he uses two models, one with time-varying parameters, and another with constant parameters. Forecasts are then based on a Bayesian model averaging strategy, which mixes forecasts from the two models. In reality, structural parameters are constant, but the (unknown) true model features expectational feedback, which the reduced-form models neglect. This feedback permits fears of parameter instability to become self-confirming. Within the context of a standard asset-pricing model, we use the tools of large deviations theory to show that even though the constant parameter model would converge to the rational expectations equilibrium if considered in isolation, the mere presence of an unstable alternative drives it out of consideration. (JEL C63, D83, D84)