Political science and international relations, like other branches of the social sciences, form a field of inquiry that is not only inseparable from complex social dynamics but is also deeply entangled with the thoughts, impulses, and decisions of individuals who do not always think or act in predictable, rational ways. In practice, when the subject of analysis is human agency and when the trajectory of events hinges on the choices of a single decision-maker, even exceptional analytical skill, long experience, and sharp intuition do not guarantee an accurate forecast. Historical Precedent: Stalin’s Miscalculation Before WWII The stakes of this uncertainty are often high. Perhaps the most instructive classic example is Stalin’s refusal to concentrate Soviet forces along the border with Nazi Germany on the eve of World War II....