Questions: Prisoner's Dilemma and Strategic Cooperation

Question 1

In a one-shot prisoner's dilemma, both players are fully rational and know the payoff structure. What should each player do?

• A. Both should defect, because defection is the dominant strategy regardless of what the other player does
• B. Both should cooperate, because rational players recognize that mutual cooperation gives the best joint outcome
• C. One should cooperate and one should defect, since this maximizes total combined utility
• D. It depends on whether the players trust each other before the game begins

Answer: (A)

Defection is a dominant strategy: regardless of what the other player does, defecting yields a higher individual payoff. If the other cooperates, defecting exploits them for a higher gain; if the other defects, defecting limits your loss. Rational players following this logic both defect — reaching the Nash equilibrium — even though both would be better off if both had cooperated. Option B describes the Pareto optimum but not what rational self-interest produces. The tragedy of the prisoner's dilemma is precisely this gap between the rational individual outcome (mutual defection) and the collectively preferred outcome (mutual cooperation).

Question 2

Why does 'tit-for-tat' succeed in the iterated prisoner's dilemma where unconditional cooperation fails?

• A. It can never be exploited, because it immediately mirrors defection while resuming cooperation when the partner does
• B. It defects randomly, keeping opponents uncertain about what to expect and discouraging exploitation
• C. It opens with defection to signal strength, then offers cooperation as a reward for good behavior
• D. It refuses to cooperate at all, converting the dilemma into a coordination game the opponent can win by cooperating

Answer: (A)

Tit-for-tat succeeds because it combines four properties: it is nice (starts cooperating), retaliatory (immediately punishes defection), forgiving (returns to cooperation once the partner cooperates), and clear (perfectly predictable). Unconditional cooperation fails because it invites exploitation — a defecting partner gains repeatedly. Tit-for-tat removes this incentive: defecting gains only one round before retaliation eliminates the advantage. The 'shadow of the future' — ongoing interaction — makes sustained cooperation individually rational.

Question 3

In a single-shot prisoner's dilemma, the Nash equilibrium produces an outcome that is worse for both players than mutual cooperation would have been.

• T. True
• F. False

Answer: True

This is the defining structure of the prisoner's dilemma. Mutual defection (the Nash equilibrium) produces payoffs that are worse for both players than mutual cooperation (the Pareto optimum). Neither player can unilaterally improve their outcome from mutual defection — that is what makes it a Nash equilibrium — but both would prefer the cooperative outcome. The game is designed so that individually rational choices produce collectively irrational results.

Question 4

The prisoner's dilemma shows that people defect because they are fundamentally selfish or irrational.

• T. True
• F. False

Answer: False

This is a common misreading. The prisoner's dilemma shows that a specific payoff *structure* drives rational agents toward defection, regardless of their character. The problem is in the incentive architecture, not in individual psychology. Real cooperation often emerges because the architecture differs from the pure one-shot game: repeated interaction, reputation, institutional enforcement, or group-level selection all change the effective payoffs in ways that make cooperation individually rational. Solutions target the structure, not the people.

Question 5

Why does 'rational self-interest' lead both players to defect in a one-shot prisoner's dilemma, even though both would be better off if both cooperated?

Model answer: Defection is a dominant strategy: it yields a higher payoff than cooperation no matter what the other player does. Each player, reasoning independently, reaches the same conclusion — and both defect. The result is the Nash equilibrium, which is worse for both than if both had cooperated. The paradox arises because the payoff structure decouples individual rationality from collective welfare: each player's best response to any action by the other is to defect, so mutual defection is stable even though mutual cooperation is preferred by both.

The key is the structure of the payoffs, not the players' values. Even two perfectly cooperative-minded players will defect if they are rational and cannot communicate or commit — because each knows the other has the same dominant incentive. The solution to the dilemma requires changing the payoff structure through repeated interaction, punishment mechanisms, or binding agreements, not appealing to the players to 'be more cooperative.'