Abstract In the context of affiliation with or withdrawing from a marginal religious group - known as “cult” by some and as “New Religious Movements” by others - it seems quite a mystery to watch an individual accept beliefs and practices perceived as irrational whereas their withdrawal is perceived as a « normal» return to their senses. We propose to examine different aspects of this change in beliefs as we address successively the affiliation process, the apparent “resistance to change” and the withdrawal from this type of movement and its beliefs. We will see that this process uses a logical rationale that can be perfectly understandable from Weber’s standpoint. A cognitive approach will help us explore the workings involved in the change of beliefs, and their effects on the reasoning capacity of the individual, by considering the alterations that happen in the thinking or “cognitive framework” of the follower.