Epictetus, Golden Sayings 89

A money changer may not reject Caesar's coin, nor may the seller of herbs, but must, when once the coin is shown, deliver what is sold for it, whether he will or no. 

So is it also with the Soul. Once the Good appears, it attracts towards itself; evil repels. But a clear and certain impression of the Good the Soul will never reject, any more than men do Caesar's coin. On this hangs every impulse alike of Man and God.