<p>Although Arthur Schopenhauer is not widely recognized as a contributor to the philosophy of mysticism, his metaphysical system anticipates several key concerns in contemporary debates about mystical experience–particularly the epistemic status of mystical reports and whether mystics share a common experience across time and cultures. Schopenhauer draws from a diverse range of mystical sources across Western and Eastern traditions, yet he does so not as a disciple of mysticism, but as a philosopher seeking external validation for his metaphysical doctrine of the blind, arbitrary Will. This raises a critical question: how does Schopenhauer respond when a mystic–such as Plotinus–offers an interpretation of ultimate reality that is neither arbitrary nor blind? This article examines Schopenhauer’s demarcation between philosophy and mysticism, wherein mystical insights are deemed incommunicable and epistemically private, while philosophical claims are presented as objective and universally debatable. By engaging closely with Plotinus’ <i>Enneads</i>, this paper challenges the coherence of Schopenhauer’s boundary. It argues that Plotinus’ metaphysical arguments are not reducible to private mystical insight and thus resist Schopenhauer’s attempt to marginalize them. In doing so, this paper reveals that Schopenhauer’s boundary between philosophy and mysticism may not withstand scrutiny, and that Plotinus’ views deserve reconsideration as legitimate philosophical contributions rather than mystical anomalies.</p>