Why do generals make sensible decisions that help achieve operational effectiveness in some cases, yet misjudge the odds and make the wrong choices in others? Generalship is a core dimension of the art of war, but its relative importancefor military effectiveness is theoretically contested and empirically unresolved. The overconfidence model and the recognition-primed decision model, two of the most influential perspectives about judgement and decisions in cognitive psychology, provide contrasting insights into the effect of generalship on military effectiveness. To assess these two models, I select a central puzzle in the history of command: General Douglas MacArthur’s success at Inchon followed a few weeks later by the stunning failure of his drive to the Yalu.