There is a sociological and cultural evidence (think of Saint Paul or contemporary online radical communities) suggesting a link between conversion and fanaticism. Profoundly revising our views about politics, ethics, or religion often go hand in hand with overconfidence in our epistemic achievements. It may even lead us to dismiss other people’s epistemic merits. The paper examines paths that cause a neophyte to become fanatic. This can happen by taking revision as a sign of invested epistemic resources, by attributing epistemic vices (such as wilful ignorance) to agents with unrevised beliefs, or by thinking other people should follow one’s conversion narrative. The paper claims that while the ability to revise one’s beliefs is a bona fide epistemic virtue, we should pay attention to undue confidence that may result from such revision.