Letters 115.18

So philosophy can settle this problem for you, and afford you, to my mind, the greatest boon that exists—absence of regret for your own conduct. This is a sure happiness; no storm can ruffle it; but you cannot be steered safely through by any subtly woven words, or any gently flowing language. Let words proceed as they please, provided only your soul keeps its own sure order, provided your soul is great and holds unruffled to its ideals, pleased with itself on account of the very things which displease others, a soul that makes life the test of its progress, and believes that its knowledge is in exact proportion to its freedom from desire and its freedom from fear. Farewell.

Seneca, Letters to Lucilius 115.18, translated by Richard Mott Gummere