Opposing the tendency to read Thucydides as a strong realist, committed to a theory of behaviour that assumes rationality as expected utility maximization, Ned Lebow and Clifford Orwin emphasize Thucydides’ attentiveness to deviations from rationality by individuals and states. This paper argues that Thucydides grasped the principles underlying contemporary prospect theory, which explains why people over-weight small probabilities and under-weight near certain ones. Thucydides offers salient examples of excessive risk-aversion in the face of probable gains and excessive risk-seeking by decision-makers (...) faced with high probability losses. Thucydides suggests that in a democracy, leaders’ rhetoric can limit or exacerbate the political effects of bias in risk assessment. (shrink)