Diagnostic errors account for more than 8% of adverse events in medicine and up to 30% of malpractice claims. Mechanisms of errors may be related to the working environment but cognitive issues are involved in about 75% of the cases, either alone or in association with system failures. The majority of cognitive errors are not related to knowledge deficiency but to flaws in data collection, data integration, and data verification that may lead to premature diagnostic closure. This paper reviews some aspects of the literature on cognitive psychology that help us to understand reasoning processes and knowledge organisation and summarises biases related to clinical reasoning. It reviews the strategies described to prevent cognitive diagnostic errors. Many approaches propose awareness and reflective practice during daily activities, but the improvement of the quality of training at the pre-graduate, postgraduate and continuous levels, by using evidence-based education, should also be considered. Several conditions must be fulfilled to increase the understanding, the prevention, and the correction of diagnostic errors related to clinical reasoning: physicians must be willing to understand their own reasoning and decision processes; training efforts should be provided during the whole continuum of a clinician's career; and the involvement of medical schools, teaching hospitals, and medical societies in medical education research should be increased to improve evidence about error prevention.