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Attributed to Zeno of Citium in Diogenes Laertius's account of Stoic epistemology (Book VII). The Stoics developed a sophisticated theory of knowledge centred on the kataleptic impression (phantasia kataleptike) — an impression of such clarity and distinctness that it compels assent and cannot arise from a false object. Self-deception (apatein heauton) was considered a fundamental epistemic and moral failure because it prevents the wise person from forming such reliable impressions. Epictetus later identified false assent — agreeing with impressions that have not been properly tested — as the root of all error and unhappiness.