Letters 95.34

Amid this upset condition of morals, something stronger than usual is needed,—something which will shake off these chronic ills; in order to root out a deep-seated belief in wrong ideas, conduct must be regulated by doctrines. It is only when we add precepts, consolation, and encouragement to these, that they can prevail; by themselves they are ineffective.

Seneca, Letters to Lucilius 95.34, translated by Richard Mott Gummere