Decision theory is enough to advise actions—so why do we need game theory? A game theory is really just a theory about the distribution over how other agents think. Given such a distribution, decision theory is enough to tell you what to do. So any simple game theory, one that claimed with certainty that all other agents always think a particular way, must be wrong. Of course sometimes a simple game theory can be good enough—if slight variations from some standard way of thinking doesn’t make much difference. But when small variations can make large differences, the only safe game theory is a wide distribution over the many ways other agents might think.
Decision theory is enough to advise actions—so why do we need game theory? A game theory is really just a theory about the distribution over how other agents think. Given such a distribution, decision theory is enough to tell you what to do. So any simple game theory, one that claimed with certainty that all other agents always think a particular way, must be wrong. Of course sometimes a simple game theory can be good enough—if slight variations from some standard way of thinking doesn’t make much difference. But when small variations can make large differences, the only safe game theory is a wide distribution over the many ways other agents might think.