Game theory studies how rational agents make decisions when outcomes depend on what others do. A zero-sum game means the total payoff is fixed—for every dollar won, someone loses a dollar. Poker is zero-sum. The stock market broadly isn’t (companies create value over time). Crypto trading? Mostly zero-sum. When you profit from a memecoin pump, that money comes from whoever bought later. Exchanges extract fees from both sides, making it negative-sum for traders collectively. Proof-of-stake and mining are also game-theoretic designs—Nakamoto consensus is a coordination game where the Nash equilibrium is “everyone follows the rules.” Understanding whether you’re in a zero-sum, positive-sum, or negative-sum game is the first step to knowing if you have an edge.