In a society increasingly bombarded by contrasting information, the question of how to interpret reality has become more and more important. This same question, though in a vastly different setting, also existed in the times of Evagrius of Pontus, a fourth-century desert father who was later condemned for his speculative teachings. In the writings of Evagrius, we see his profound fascination with the problem of delusion: of whether one’s experience or interpretation of reality can be trusted. This problem is at the heart of this study, where the author argues that Evagrius’ accounts of the vision of the light of the Holy Trinity cannot be properly understood without also taking into account his warnings against delusion.