John Nash was awarded the 1994 Nobel Memorial Prize in Economic Sciences for an idea he first set out as a young mathematician: the Nash equilibrium. It describes a stable point in any game of strategy where no player can do better by changing their move alone, given what everyone else is doing.
Before Nash, game theory largely handled head-to-head, zero-sum contests. His insight generalised the field to situations where players cooperate or compete in complex ways — from arms races and auctions to market competition and evolutionary biology.
The concept became one of the most widely used tools in modern economics precisely because it makes strategic behaviour predictable: find the equilibrium, and you have a good guess at where rational players will end up.
Why it matters: The Nash equilibrium turned "what will everyone do?" into a question you can actually solve — the foundation of modern game theory.
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