Realpolitik, the pursuit of vital state interests in a dangerous world that constrains state behavior, is at the heart of realist theory. All realists assume either that states engage in such behavior or, at the very least, are highly incentivized to do so by the structure of the international system. Classical realists remind us, however, that Realpolitik presupposes rational thinking, which should not be taken for granted. Some leaders act more rationally than others because they think more rationally than others. Research in cognitive psychology provides a strong foundation for classical realist claims that Realpolitik requires a commitment to objectivity and deliberation, a particular psychology that few leaders exhibit. A case study of Otto von Bismarck's role in German reunification demonstrates that rationality is the exception, rather than the norm. Even though Prussia was under enormous structural constraints that should have incentivized Realpolitik, the man who would become the Iron Chancellor was isolated because of his foreign policy views. Bismarck consistently disagreed with conservative patrons and allies at home, disagreements that can be reduced largely to his higher degree of rationality.

中文翻译：

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现实政治的稀有性：俾斯麦的理性揭示了国际政治

现实政治，即在限制国家行为的危险世界中追求重要的国家利益，是现实主义理论的核心。所有现实主义者要么假设国家从事此类行为，要么至少受到国际体系结构的高度激励。然而，古典现实主义者提醒我们，现实政治以理性思维为前提，这不应被视为理所当然。有些领导者的行为比其他人更理性，因为他们比其他人思考得更理性。认知心理学研究为经典现实主义主张提供了坚实的基础，即现实政治需要对客观性和深思熟虑的承诺，这是很少有领导者表现出的特殊心理学。奥托·冯·俾斯麦在德国统一中的作用的案例研究表明，理性是例外，而不是常态。尽管普鲁士受到巨大的结构性限制，本应激励 Realpolitik，但这位后来成为钢铁大臣的人因其外交政策观点而被孤立。俾斯麦一贯不同意国内的保守派赞助人和盟友，这种分歧在很大程度上可以归结为他的更高程度的理性。