Applications of the maximin criterion extend beyond economics to statistics,
computer science, politics, and operations research. However, the maximin
criterion---be it von Neumann's, Wald's, or Rawls'---draws fierce criticism due
to its extremely pessimistic stance. I propose a novel concept, dubbed the
optimin criterion, which is based on (Pareto) optimizing the worst-case payoffs
of tacit agreements. The optimin criterion generalizes and unifies results in
various fields: It not only coincides with (i) Wald's statistical
decision-making criterion when Nature is antagonistic, (ii) the core in
cooperative games when the core is nonempty, though it exists even if the core
is empty, but it also generalizes (iii) Nash equilibrium in n-person
constant-sum games, (iv) stable matchings in matching models, and (v)
competitive equilibrium in the Arrow-Debreu economy. Moreover, every Nash
equilibrium satisfies the optimin criterion in an auxiliary game