Cognitive errors underlie most diagnostic errors that are made in the course of clinical decisionmaking in the emergency department. These errors are universal and are prevalent in the special milieu of the ED. Their properties appear to be distinct from those associated with the performance of procedures. They are often costly, but, importantly for both the patient and the physician, they are also highly preventable. Recent developments in education theory provide a means for minimizing and avoiding diagnostic error. Through the process of metacognition, clinicians can develop cognitive forcing strategies to abort such latent errors. Three levels of cognitive forcing strategies are described: universal, generic, and specific. Specific cognitive forcing strategies provide a formal cognitive debiasing approach to deal with what have previously been described as pitfalls in clinical reasoning. This metacognitive approach can be taught to practicing clinicians and to those in training to inoculate them against making diagnostic errors. The adoption of this method provides a systematic approach to cognitive root-cause analysis in the avoidance of adverse outcomes associated with delayed or missed diagnoses and with the clinical management of specific cases.