Dominant Strategy
A dominant strategy is a choice that produces the best available outcome for a player regardless of what the other player does. You don't need to know or predict the opponent's move — the dominant strategy is optimal against every possible opponent action.
In the one-off prisoners-dilemma, defecting is dominant: if the opponent cooperates, you're better off defecting (you get 5 instead of 3); if the opponent defects, you're still better off defecting (you get 1 instead of 0). Defecting wins both cases.
The disturbing implication: when both players follow their dominant strategy, they produce a collectively worse outcome (both get 1) than if neither had (both get 3). Individual rationality aggregates into collective irrationality.
Limits
Dominant strategies only exist in this clean form in simple, symmetric, one-off games. Most real situations are:
- Iterated — repeated over time, which changes the payoffs entirely (see iterated-games)
- Asymmetric — players have different options, costs, or information
- Multi-player — coalitions and third-party effects complicate the calculus
In those cases there may be no dominant strategy, and players must reason about what opponents are likely to do — which is where game theory becomes genuinely complex.
Connections
- prisoners-dilemma — the classic case where the dominant strategy exists but leads to a bad collective outcome
- iterated-games — repeated interaction eliminates the clean dominance of defecting; tit-for-tat wins where pure defection fails