The trust game captures an essential dilemma of human sociality.

Betrayal becomes more poignant if it occurs after promises were made.

Trustors do well being mindful of the trustee’s incentives to defect.

The best way to find out if you can trust somebody is to trust them. —Hemingway

Interpersonal trust, along with the disappointments that occasionally occur, lies at the heart of human sociality. To understand its challenges and how ordinary people navigate the landscape of social uncertainty is one of the main tasks of social psychology.

Psychologists and behavioral economists have turned to a stylized experimental game to capture the essential elements of trust, that is, its necessary and sufficient characteristics (Berg et al., 1995). In this game, a trustor receives a small endowment of $10. If they transfer the money to a trustee, its value is multiplied, and the trustee then chooses between keeping it all—and thank you very much indeed!—and sharing the newfound wealth equitably with the trustor. Whereas the trustee merely needs to choose between self-regard and reciprocity, the trustor faces a decision under uncertainty. There are no clear paths leading to an optimal decision, but trustors can use a set of social heuristics to navigate this uncertain space (Krueger et al., 2026).

This trust game is an abstraction, and as such, it reflects a bare-bones sort of social ecology. In its canonical form, the two players do not know each other, they do not know how their roles were assigned, and they have no expectation to play with each other ever again. There is also the interesting convention that the trustor makes the first move by either transferring the money or by walking away with the small gain of........

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