Uncertainty is unavoidable in health care, yet frequently tacit. When uncertainty is acknowledged, it tends to be defined in terms of the unpredictable nature of the care, and limits to human knowledge. It is cast as a problem that evidence-based health care can minimize. Challenging that simplistic perspective, this paper reconstructs uncertainty as a property whose meaning derives from how people are relationally disposed to perceive it in the social context in which they are embedded. Five conditions are suggested to define a need to protect and cultivate uncertainty as a virtue or positive disposition. These conditions are that uncertainty is natural, promotes creativity and a critical attitude, can signify wisdom, nurtures safety, sustains hope and protects against excess. In contrast, certainty is a delusion. Believing in certainty is unscientific and antiscientific because it can obscure and devalue critique in scientific practice.