game theory in markets tit for tat and cooperation

Every trade you take is a game. The other participants are players. Their decisions affect your outcomes and yours affect theirs. Game theory — the study of strategic decision-making — provides a framework for understanding why markets behave the way they do and why certain strategies are sustainable while others aren’t.

see also: gn12-extremistan-vs-mediocristan · skin-in-the-game-trading · gn09-second-order-thinking

zero-sum vs positive-sum

Not all trading is the same game. Futures and forex are approximately zero-sum — for every winner, there’s a loser. Equities are positive-sum over the long run because companies create value. Crypto is debated — some say zero-sum, others argue it creates value through network effects.

Understanding which game you’re playing changes everything. In a zero-sum game, your edge must come from being better than the other players. In a positive-sum game, you can win simply by participating and holding.

The mistake: treating a positive-sum game as zero-sum (overtrading, short-term focus) or treating a zero-sum game as positive-sum (holding losing positions hoping for recovery).

the iterated prisoner’s dilemma

The classic game theory problem: two criminals are arrested. Each can either stay silent (cooperate) or betray the other (defect). If both stay silent, both get minor sentences. If one betrays and the other stays silent, the betrayer goes free and the silent one gets the maximum. If both betray, both get moderate sentences.

In a one-shot game, betrayal is the rational choice. In an iterated game — where players interact repeatedly — cooperation becomes rational because defection is punished in future rounds.

tit for tat

Robert Axelrod’s tournament tested strategies for the iterated prisoner’s dilemma. The winner was the simplest: Tit for Tat.

1. Start by cooperating
2. Copy your opponent’s previous move
3. Forgive after one punishment

Tit for Tat works because it’s nice (never defects first), retaliatory (punishes defection immediately), forgiving (returns to cooperation if the opponent does), and clear (opponents understand the pattern immediately).

application to trading

Markets are iterated games. The same participants trade against each other repeatedly. Reputation matters. Being known as a reliable counterparty has value. Burning bridges for a single trade is rarely optimal.

Practical implications:

• Market makers use Tit for Tat — they provide liquidity (cooperate) but widen spreads when takers are toxic (punish defection)
• Institutional traders build relationships with brokers — defecting (trading around them, burning them on information) destroys long-term access
• Retail vs institutional is a one-shot game for retail (they don’t interact with the same institution repeatedly) but iterated for institutions (they see each other in the flow every day)

my take

I think about game theory most when deciding how to interact with the market. Trend following is essentially a cooperative strategy — you’re providing liquidity to trend, not fighting the flow. Mean reversion is more competitive — you’re betting against the marginal buyer/seller.

The most dangerous situation is playing an iterated game with one-shot mentality. The trader who blows up their account is defecting against their future self — they’re burning capital they’ll need for the next trade, the next week, the next year.

The market remembers. Not literally — but the consequences of your decisions compound. Every trade that’s too large, every risk taken without a stop, every revenge trade after a loss — these are defections against your own long-term survival.

linkage

• [[gn12-extremistan-vs-mediocristan]]
• [[skin-in-the-game-trading]]
• [[gn09-second-order-thinking]]
• [[gn10-inversion]]

ending questions

are you playing a zero-sum or positive-sum game? if your strategy depends on being smarter than everyone else, what happens when smarter money enters?