Letters 95.40

Furthermore, precepts will perhaps help you to do what should be done; but they will not help you to do it in the proper way; and if they do not help you to this end, they do not conduct you to virtue. I grant you that, if warned, a man will do what he should; but that is not enough, since the credit lies, not in the actual deed, but in the way it is done.

Seneca, Letters to Lucilius 95.40, translated by Richard Mott Gummere