Letters 75.10

Some define this class, of which I have been speaking,—a class of men who are making progress,—as having escaped the diseases of the mind, but not yet the passions, and as still standing upon slippery ground; because no one is beyond the dangers of evil except him who has cleared himself of it wholly. But no one has so cleared himself except the man who has adopted wisdom in its stead.

Seneca, Letters to Lucilius 75.10, translated by Richard Mott Gummere