Letters 95.4

But I must stop this preamble and approach the problem under consideration. Men say: “The happy life consists in upright conduct; precepts guide one to upright conduct; therefore precepts are sufficient for attaining the happy life.” But they do not always guide us to upright conduct; this occurs only when the will is receptive; and sometimes they are applied in vain, when wrong opinions obsess the soul.

Seneca, Letters to Lucilius 95.4, translated by Richard Mott Gummere