Costly punishment frequently occurs in social relationships. Yet, incurring costs does not always have direct benefits. For example, breaking up with one’s partner after observing a one-off infidelity can induce emotional, social, and economic damage without the prospect of a better future. Why, then, choose to know?

The idea that humans are curious has deep roots in Western philosophy. Aristotle, for instance, opened Metaphysics with the words: “All men, by nature, desire to know”. Knowledge is valued and sought – the human thirst for it seems to be insatiable. Yet, individuals often choose not to know.

Deliberate ignorance – defined as the conscious choice not to seek or use information – is prevalent in human behavior. The reasons are diverse. They range from emotion regulation to performance enhancement. Not knowing can, for example, allow individuals to avoid regret and effectively cope with arousal in comparisons with rivals. We focus on deliberate ignorance as a profoundly social phenomenon.

Deliberate ignorance can be used as a strategic device. Labor union leaders may, for example, refrain from meeting with their members to convey to management that a strike will only conclude with a more favorable offer. Since Nobel Prize-winning economist Thomas Schelling published An Essay on Bargaining in 1956, economists have been intrigued by how negotiators can leverage deliberate ignorance to gain bargaining power.

The Ultimatum Game is a common tool for studying bargaining behavior. In the game, one person (the proposer) receives a sum of money and proposes how to split it with another person (the responder). If the responder accepts the offer, the proposed split is implemented; if not, both players receive nothing. In the standard version, the responder knows how much money the proposer has received, and unequal offers are frequently rejected. For example, responders who have been offered $1, knowing that a proposer has received $10, often reject the offer. This finding has been interpreted as a preference for equality, as offers heavily favoring the proposer, at the expense of the responder, can be perceived as unfair. Many responders punish such behavior by opting for an outcome where both players receive nothing, rather than accepting an unfair offer.

Responders cannot ignore inequality in the standard version of the Ultimatum Game. When they receive an offer, they know whether the proposed split is equal or not. Yet, responders may not want to know about potential inequality since knowledge can come at a cost: It may induce an urge to punish. If responders anticipate the urge, but still want the money, they might prefer not to learn about the proposer’s endowment.

We conducted an experiment where responders could deliberately ignore inequality in the Ultimatum Game. Specifically, responders could choose not to know whether they had received a fair or an unfair offer before accepting or rejecting it. Some responders had, for example, been offered 10¢ without knowing whether the proposer had received 20¢ (representing a fair offer) or 100¢ (representing an unfair offer). The responders could reveal the proposer’s endowment by clicking a button. Requesting information was free of charge. We hypothesized that deliberately ignorant responders would be less likely to reject unfair offers compared to actively informed responders. Additionally, we anticipated a lower probability of punishment in environments with uncertainty about inequality, as opposed to environments where information was directly provided (i.e., where responders were passively informed about inequality).

We found that 53% of responders deliberately ignored inequality. Among these responders, only 6% of unfair offers were rejected. As hypothesized, participants who actively sought information rejected significantly more offers (39%). Averaging these rejection rates to 21% revealed no significant difference compared to the rejection rate of responders who were directly informed about inequality, contrary to our expectation. We interpret our findings as evidence for sorting behavior: Some individuals reveal inequality and subsequently punish, whereas others deliberately ignore it and avoid inflicting costs.

Our data suggest that a substantial proportion of individuals may choose not to know about inequality, and that sorting behavior may play an important role in real-world punishment behavior. Specifically, we interpret deliberate ignorance in our findings in terms of emotion regulation and as a strategic device for the preservation of self-esteem. Choosing not to know that one has been treated unfairly may allow individuals to anticipate and counter possible anger, resentment, or regret. Maintaining positive self-esteem, individuals may accept possibly unfair offers at lower emotional costs and at reduced levels of cognitive dissonance. For instance, turning a blind eye to a one-off infidelity may reduce the urge to induce emotional, social, and economic costs both on one’s partner and on oneself.

Our Registered Report is one of the first two Stage 2 Registered Reports co-published by Communications Psychology. The Registered Report process allowed us to increase the methodological rigor of our work. For example, feedback from both editors and reviewers enabled us to base our effect size estimates on more solid footing. This, in turn, enhanced our power analysis, increasing the rigor in our sample size calculations, which we openly shared during our Stage 1 review process. We are grateful for how Communications Psychology has supported the Registered Report process and open science practices during our research project.

Psychologists have for long been interested in knowledge acquisition and human curiosity. Many questions about deliberate ignorance remain. Building upon the strengths of Registered Reports, we have examined whether people avoid the urge to reject unfair offers by deliberately ignoring unfairness. Our findings suggest that not all people want to know about inequality, and that some individuals reveal inequality and subsequently punish, while others deliberately ignore it without imposing costs. We see deliberate ignorance as a promising field to work together across disciplines, such as psychology, economics, law, and philosophy to better understand human behavior and the desire not to know.