This chapter begins the second part of the book, dedicated to demonstrating that even the most established assumptions about the law can be replaced if another assumption would lead to hypotheses that are better confirmed by legal sources. The chapter is focused on the assumption of proportionality, a principle that is shown to explain well many doctrines in the laws of war, domestic criminal law, and international sales law. The chapter also shows that in situations of acute uncertainty, the law does not support immediate and proportional responses and allows instead delayed and disproportional responses. Proportional responses concur with the tit-for-tat strategy which makes them useful at limiting disputes when there is no uncertainty, according to experimental game theory. In contrast, in situations of uncertainty, a strategy of delayed and disproportional responses—like the one adopted by different legal regimes in this condition—is more effective. The law is therefore not committed to proportionality at all costs and can turn to disproportional responses in some cases to secure better results.