 The vNM theorem is a very important result for measuring the strength of a rational agent’s preferences over sure options (the lotteries effectively facilitate a cardinal measure over sure options). But this does not get us all the way to making rational decisions in the real world; we do not yet really have a decision theory. The theorem is limited to evaluating options that come with a probability distribution over outcomes—a situation decision theorists and economists often describe as “choice under risk” (Knight 1921).