Game Theory
Tit-for-Tat
Two men sit knee to knee at a narrow table. One smiles first, palm open over the center line, a coin glinting on his skin. The room is quiet enough to hear the chair legs rasp. A dotted seam splits the space between them; small equations ghost the wallpaper like chalk after rain. The second man answers with the same small smile and nudges the coin back. Their hands become metronomes. An arrow of intention seems to shuttle in the air from face to face, passing the lead, returning it unchanged.
Tit-for-tat begins with cooperation and then copies whatever the other person just did. Help is answered with help; a slap is answered with one slap, not a vendetta. It is nice, retaliatory, and forgiving all at once: it starts warm, punishes once, and returns to open hands the moment the other does. You see it at a four-way stop, in email turn-taking, between neighbors who bring each other’s bins to the curb. The clarity is the point — your partner never has to guess what tomorrow earns.
Therefore
Begin generous; then mirror the last move — no more, no less. Reward cooperation immediately; answer defection once, and return to yes.
Axelrod and Rapoport, 1980
At the University of Michigan in 1980, political scientist Robert Axelrod ran a computer tournament of repeated Prisoner’s Dilemmas. Entrants mailed in programs with names like GRIM and JOSS, each trying to outfox the field. Anatol Rapoport sent a few lines of code: cooperate first, then copy the opponent’s previous move. That tiny entry, TIT FOR TAT, won the tournament — and then won again when Axelrod repeated it with a larger field. It did not crush enemies; it coaxed them. Against strategies willing to cooperate, it locked in mutual gain. Against cheaters, it stung once and waited for peace.
Related patterns
extends to
Coevolutionary Intertwine: Growth & Reciprocity
Reciprocal moves co-shape partners across time.
pairs with
Skin in the Game: Personal Stake & Consequence
Reciprocity works when costs land on you.
contrasts with
Schelling Point: The Obvious Meeting Place
Coordination by expectation, not remembered moves.
A small reminder, on a whiteboard or lunchroom door, that cooperation sticks when you reply in kind — smile for smile, one sting, then open again.
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