Omission bias refers to the tendency to judge the negative consequences of inaction as less blameworthy than those resulting from action, even when outcomes are equivalent and action offers a higher probability of success. This chapter illustrates this bias through the history of the management of penetrating abdominal wounds from the late nineteenth century to World War I, a period dominated by a preference for conservative treatment despite mounting evidence in favor of early laparotomy. The influence of prominent figures such as MacCormac and Treves cemented the notion that surgery was dangerous and that omission represented the “safer” option, even when outcomes indicated otherwise. The chapter reviews the definition, psychological underpinnings, and moral explanations of the bias, from the doctrine of double effect and the trolley problem to modern experiments by Ritov, Baron, and Spranca. It also addresses its impact on contemporary decisions, including vaccination, organ donation, institutional policies, and multiple clinical and surgical scenarios in which inaction is unjustifiably favored. Finally, strategies to mitigate this bias are discussed, including explicit comparison of outcomes, use of risk–benefit analysis tools, counterfactual reasoning, reframing, and deliberate active decision-making.