Year after year, thousands of human lives are permanently extinguished by large-scale events such as disasters, epidemics, and armed conflicts, while millions more are claimed by frequent small-scale events, such road accidents and fires. Preventing these fatalities should be a priority for policymakers, because death is irreversible, and survival necessarily precedes other forms of human welfare. Minimizing fatalities requires that policymakers respond to deadly events and that they effectively focus their attention, efforts, and life-saving resources on preventing the largest (aggregated) death tolls. However, the deployment of any major intervention, even one designed to save lives, requires sufficient political will, which in turn depends on people being moved to action by the number of lives at risk. All else being equal, responses to deadly events should be proportional to their potential death tolls, and support for life-saving interventions should grow steadily with the number of lives they are expected to save. Unfortunately, people's reactions to deadly events generally fall short of these principles and instead reveal systematic limitations in their ability to properly evaluate human fatalities. This article discusses some of the cognitive factors that govern, and often skew, the way people perceive and respond to deadly events. I show that our failures to correctly prioritize and address the biggest causes of human casualties are driven by limitations and biases in perception, attention, and categorization. Understanding these psychological fallibilities will help policymakers recognize, and ultimately guard against, biases that hinder the deployment of important life-saving policies.