Letters 74.30

The other answer, which I promised to make to your objection, follows from this reasoning. The wise man is not distressed by the loss of children or of friends. For he endures their death in the same spirit in which he awaits his own. And he fears the one as little as he grieves for the other. For the underlying principle of virtue is conformity; all the works of virtue are in harmony and agreement with virtue itself. But this harmony is lost if the soul, which ought to be uplifted, is cast down by grief or a sense of loss. It is ever a dishonour for a man to be troubled and fretted, to be numbed when there is any call for activity. For that which is honourable is free from care and untrammelled, is unafraid, and stands girt for action.

Seneca, Letters to Lucilius 74.30, translated by Richard Mott Gummere