The appropriate response to human shields is a recurring issue in modern warfare. Technological asymmetry, disparate obligations, and doctrinal divergence between state and nonstate adversaries combine to make civilians account for 84 percent of combat deaths. Just as a slot machine entices a gambler though he rarely wins, the international community’s inconsistent response to human shields has placed shield users on an intermittent reinforcement schedule, thereby ensuring that this tactic remains part of insurgent strategy. Long-term protection of civilians requires eliminating this tactic. Principles of behavior science indicate that an effective way to do so is to uniformly remove its desired consequence— combatants must never allow the presence of shields to impede access to the shielded military objective. This approach is supported by a broader, more forward-thinking conception of the principle of proportionality as reflected in current treaty and customary international law.