Psilocybin has repeatedly been shown to trigger mystical-type experiences, and brain science is beginning to explain why. Classic experiments found that 30–40% of participants given psilocybin met criteria for a complete mystical experience, while modern replications reported rates as high as 61%, compared to 11% or less in control conditions. Two months later, 71% of participants rated the experience as one of the most spiritually meaningful events of their lives, with effects persisting for over a year. Using Bayesian brain theory, this paper explains these experiences as a temporary loosening of rigid mental predictions, allowing sensory input to dominate. This shift is linked to feelings of unity, loss of ego boundaries, altered time perception, deep insight, and lasting positive mood, offering a scientific framework for why psilocybin experiences often feel “realer than real” and remain meaningful long after the session ends.