This publication is a continuation of the article published in the 4th issue of the journal Russian family doctor for 2020 Heuristics, language and medical errors, which described the ways of making medical decisions that can lead to errors in patient management tactics, in particular affect of heuristics / visceral bias, attribution error, frame of reference, availability bias, one-word-one-meaning-fallacy. This article discusses additional sources of diagnostic error, including diagnosis momentum, confirmation bias, representativeness, and premature closure also the conflict that arises from diagnostic uncertainty is discussed. All errors in the tactics and the diagnostic process are illustrated by clinical cases from the personal practice of the author of the article.