Assuming one person's gain must come at another's expense, even in situations where everyone could benefit.
Imagine you and your friend both want cookies, and you think there are only 10 cookies in the whole world. If your friend gets 3, you think that means you can only get 7. But actually, someone is baking more cookies all the time! Zero-sum bias is when you think someone else winning means you're losing, even when there's plenty for everyone.
Zero-sum bias describes the cognitive tendency to frame interactions, resource distributions, and social outcomes as inherently competitive, even when the situation objectively allows for shared gains. People exhibiting this bias assume that any benefit obtained by another person or group must be accompanied by an equivalent loss to themselves or their group, treating life as though all resources exist in a fixed pool. This bias is especially pronounced when desirable resources are being allocated and when people perceive themselves in competition with out-groups. It undermines cooperation, fuels intergroup hostility, and prevents individuals from recognizing or pursuing mutually beneficial solutions that would leave all parties better off.
The same glitch looks different depending on the terrain. Finance, medicine, a relationship, a team — same mechanism, different costume.
Investors and the public often view international trade as inherently win-lose, believing that a trade surplus for one country must mean a deficit-driven loss for another, which leads to resistance against free trade agreements even when both economies would grow from the exchange.
Patients may resist organ donation programs or public health resource allocation if they believe that directing medical resources toward one group of patients necessarily deprives their own group of care, even when total healthcare capacity is expandable.
Daniel V. Meegan formally introduced the term 'zero-sum bias' in a 2010 paper published in Frontiers in Psychology. The broader concept of zero-sum thinking draws on game theory foundations laid by von Neumann and Morgenstern (1944) and was elaborated cross-culturally by Różycka-Tran, Boski, and Wojciszke in their 2015 37-nation study.
In ancestral environments, critical resources like food, mates, territory, and social status were genuinely scarce and often truly zero-sum. An individual who failed to recognize and respond to competitive resource dynamics risked losing survival-critical resources. A cognitive bias toward assuming competition — even when occasionally wrong — was less costly than failing to compete when resources were truly limited. The slow pace of technological progress during human evolution meant no individual would have observed resource growth in their lifetime, making zero-sum the rational default model.
When training data reflects zero-sum social dynamics — such as historical hiring data where one demographic's advancement correlated with another's decline — ML models can encode and perpetuate these competitive assumptions as if they are causal rules rather than artifacts of past discrimination. Recommendation algorithms may also exhibit zero-sum patterns by treating user engagement as a fixed resource, aggressively competing content against itself rather than expanding total engagement time.
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