dominant strategy
/ DOM-uh-nunt STRAT-uh-jee /
Sometimes a strategic puzzle has a delightfully simple answer: one of your options is better than the others no matter what anyone else does. You don't even need to guess your opponent's plan — you just play your best move and be done. That is a dominant strategy: a choice that gives you at least as good a payoff as your other choices, against every possible thing the other players might do.
Concretely, compare two of your options across every column of the payoff matrix (every possible rival move). If option A always pays you more than option B, then B is 'dominated' and A 'dominates' it. A strategy that dominates all your alternatives is your dominant strategy. Example: suppose pricing Low earns a firm more than pricing High whether the rival prices Low (8 vs 5) or High (12 vs 10). Then Low is dominant — the firm should price Low without needing to predict the rival at all. Economists also speak of weak dominance, where your option is at least as good and sometimes strictly better.
Dominant strategies are precious because they make analysis easy and predictions confident — a rational player will always use one if it exists. They are also the engine of the prisoner's dilemma, where 'confess' is each prisoner's dominant strategy, which is exactly why both end up worse off. The catch: most interesting games have no dominant strategy at all. When your best move genuinely depends on the other player's move, you must fall back on the broader idea of Nash equilibrium.
Whether or not it rains, you are better off carrying a small umbrella than a heavy one — light if it stays dry, still dry if it pours. Since the small umbrella beats the heavy one in every weather, carrying the small umbrella is a dominant strategy: you can decide without checking the forecast.
A choice that wins in every state of the world is a dominant strategy — no forecast required.
Every dominant-strategy outcome is a Nash equilibrium, but not the reverse. And beware: most real games have no dominant strategy, so its absence is the normal case, not a sign you've made a mistake.