actions and omissions. The omission effect evaporated, with the moral weight of an action perceived to be on a par with an omission. The Mayan study is but one example. It suggests some flexibility in our perception of actions and omissions, and shows how cultural differences can create individual differences. When our social world is relatively small and circumscribed, we can keep tabs on everyone. By keeping tabs, we can hold others responsible for their actions and their omissions. As the American psychologists Jon Haidt and Jonathan Baron have shown, this psychology can be recreated in the laboratory by creating scenarios in which the individuals are either unfamiliar or familiar. When there is a relationship between the individuals — family, friends, team members — and thus, some degree of familiarity, the omission effect weakens. The omission effect is not an obligatory state of the human mind. It is a common tendency, a way that our brains lean, especially in unfamiliar contexts. In patients with obsessive compulsive disorder, the omission effect is as strong as it is in healthy subjects, except for familiar cases of harm that are directly relevant to them, such as the excessive washing behavior that is the trademark of this clinical disorder. The fact that certain situations can cause us to lean in different directions has important policy implications: even when corporations, institutions, or other organizations grow large, we should always segregate these masses into smaller divisions, and make the issues personally relevant. Every member of one division should hold all others within its division responsible or accountable. Further, efforts should be made to foster familiarity across divisions, enabling not only a level of responsibility but of respect and trust. By recreating the psychology of small scale societies, and making potential harms relevant, we may help bypass the omission effect, allowing us to hold people responsible for their omissions. Th