With adequate cost containment unlikely in the foreseeable future, health care use will have to be curtailed, ideally with open and explicit criteria for equitably allocating resources or rationing. Yet, consensus on any such criteria appears remote because Americans cannot say no to health care. Americans may refuse to accept rationing for two reasons. The absence of any global limitation on health care resources may encourage patients to believe that health care resources are not scarce and do not need to be rationed. A belief in vitalism--that everyone is morally entitled to unlimited longevity and good health--may discourage setting limits on one's own care. Together, these characteristics may foster the belief that denials of health care services, especially by health insurers, are arbitrary or unfair refusals to pay for existing resources and not a necessary method of rationing scarce resources. If this hypothesis is true, Americans are unlikely to achieve consensus on any equitable allocation of health care unless they face an actual shortage (credible scarcity) of health care resources that makes it necessary to ration care.