This article examines the relationship between cognitive biases and fanaticism, drawing on data from teachers and contemporary psychological research. In the framework of previously proposed theories (for example, the theory of “automatic decisions and biases” by Tversky and Kahneman 1974), it is argued that people use intuition and automatic rules to simplify complex information, but are prone to systematic errors as a result. The recently recognized model of “errors in the process of knowing” (discordant knowing) suggests that the mechanism of denial of contradictory information in fanatical thinking is the psychological basis. The research part analyzes the correlation between the level of cognitive biases and the observed results on fanaticism among 1st-3rd year students of the International Nordic University. The results obtained showed that fanatical thinking is higher among individuals with strong cognitive biases, which is associated with the pursuit of inconsistent knowledge in the mind and increased group identification. The article concludes with a discussion of ways to prevent fanaticism by reducing cognitive biases.