Prediction plays a vital role in every branch of our contemporary lives. While the credibility of quantitative simulations through mathematical modeling may seem to be universal, how they are perceived and embedded in policy processes may vary by society. Investigating the ecology of quantitative prediction tools, this article articulates the cultural specificity of Japanese society through the concept of Jasanoff’s “civic epistemology.” Taking COVID-19 and nuclear disasters as examples, this article examines how predictive simulations are mobilized, contested, and abandoned. In both cases, current empirical observation eventually replaces predictive future simulations, and mechanical application of preset criteria substitutes political judgment. These analyses suggest that the preferred register of objectivity in Japan—one of the constitutive dimensions of civic epistemology—consists not in producing numerical results, but in precluding human judgment. Such public calls to eliminate human agency both in knowledge and in policy-making can be a distinct character of Japanese civic epistemology, which may explain why Japan repeatedly withdraws from predictive simulations. It implies the possibility that Western societies’ faith in human judgment should not be taken for granted, but explained.