Over the past two decades, the risk analysis community has made substantial advances in understanding and describing uncertainty. Uncertainty is ubiquitous, complex, both quantitative and qualitative in nature, and often irreducible. Uncertainty thus creates a challenge when using risk analysis to evaluate the rationality of group and individual decisions. We may assume that calculated risk estimates adequately represent "true risk," and portray technically trained risk analysts as the arbiters of truth. An unfortunate consequence of this results when an individual or group is thought to deviate from a "rational" course of action, as determined by risk analysis, when in fact the individual or group is behaving rationally. This rationality could be due to a more complete understanding of the risk, reasonable distrust of the presumptive experts, or both. This article discusses how uncertainty can lead to incorrect calculations of risk, and how those calculations can lead to inappropriate assessments of irrational action. Examples are used to illustrate possible effects. Individuals tasked with diagnosing individual reactions to risk situations should be able to differentiate between "calculated," "perceived," and "true" risk. (Contains 1 table.)