Repeated Games & Cooperation

Repeated Games and Cooperation · Open board

The Prisoner's Dilemma left two rational people trapped in mutual betrayal, in a single sealed-room round. This board is the escape hatch: let the same two people meet again and again, with nothing else changed, and the very same selfish players find their way to trusting each other.

Before you start. The Prisoner's Dilemma found the trap: questioned once, in separate rooms, ratting out your partner beats staying silent no matter what they do, so both rational players land on the outcome they’d both hate. This lesson keeps the same two numbers and asks what changes once they know they’ll be questioned again next week.

The idea in 30 seconds

Two rational, purely selfish players can end up cooperating once they expect to meet again - the future cost of being punished later, the shadow of the future, makes betraying someone today expensive.
In Robert Axelrod’s 1980 computer tournament of repeated betray-or-trust games, the simplest rule won: cooperate first, then copy the other side’s last move - nice, quick to retaliate, forgiving, and easy to read.
A relationship with a known end date collapses backward from the last day to the first, so lasting cooperation needs a future that’s never definitely over.
Repetition makes cooperation possible; it doesn’t make it the only stable outcome - culture and coordination decide which arrangement holds.
One misread move between two players who each copy the other’s last move starts an endless run of alternating payback; a rule that sometimes cooperates anyway breaks it.
Reputation extends the same trust to strangers you’ll never personally meet twice.

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