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Prisoner's Dilemma (One-Shot): Why Defection Comes First

The one-shot Prisoner's Dilemma captures the non-trivial core of cooperation.

Each player has two actions:

  • C: cooperate
  • D: defect

Canonical payoff ordering:

T > R > P > S

Where:

  • T (temptation): payoff for defecting against a cooperator
  • R (reward): payoff for mutual cooperation
  • P (punishment): payoff for mutual defection
  • S (sucker): payoff for cooperating against a defector

Defection Is the Dominant One-Shot Strategy​

For each player, D yields a higher immediate payoff regardless of the other player's action:

  • if the opponent cooperates, defecting gives T > R
  • if the opponent defects, defecting gives P > S

So in one-shot play, rational best response is defection.

Why This Matters for Learned Cooperation​

If defection is the local optimum, then cooperation cannot be assumed. It needs a mechanism. That mechanism often comes from repeated interaction, memory, and contingent responses.

Next step: Iterated Prisoner's Dilemma