Stoic Sages never make mistakes. Secure in their understanding of the providential structure of the world, which is identical with fate, which in turn is identical with the will of Zeus (DL VII 135, =SVF 2.580; Plutarch, St. rep. 1049f, 1056c = SVF 2.937; cf. 2.931, 2.1076), Sages order their lives in accordance with it, assimilating their will to the will of Zeus, living in accordance with nature, and so achieving the smooth flow of life, the eurhoia biou so devoutly to be wished for (DL VII 87, =SVF 3.4; Cicero, Fin. III 31, IV 14-15, =SVF 3.15, 3.13; cf. 3.4-9, 3.12-16).

It seems clear enough that if the Sage is to be anything more than an unattainable, regulative ideal (and that is a big ‘if’), the Stoics need powerful reasons, in the form of a powerful epistemology, for supposing that such practical infallibility can ever actually be attainable. And even if the Sage is supposed only to be an ideal figure (and the Stoics were doubtful whether such a superhuman ethical cognizer ever had existed: Sextus, M IX 133, =54D LS; Alexander, Fat. 199.16, =SVF 3.658, =61N LS), still, for the ideal to function as anything more than a piece of remote wishful thinking, it had better be possible at least to approach that ideal; and the Stoics did indeed set great store by the notion of prokopê, moral and cognitive progress (Stobaeus V 906.18–907.5, =SVF 3.510, =59I LS).