Among those who criticize the concept of ‘medical futility,’ a common refrain is that we really have no idea what futility means. For example, physicians seem to disagree on whether a treatment being futile means that it has a less than 5% chance of working or a 20% chance of working. If the concept is so unclear, then it seems a thin reed upon which to base a momentous ethical decision—namely, that the physician's judgment should be allowed to override the wishes of the competent patient or the patient's duly appointed surrogate.