Letters 85.37

but the wise man is not harmed by poverty, or by pain, or by any other of life’s storms. For all his functions are not checked, but only those which pertain to others; he himself is always in action, and is greatest in performance at the very time when fortune has blocked his way. For then he is actually engaged in the business of wisdom; and this wisdom I have declared already to be, both the good of others, and also his own.

Seneca, Letters to Lucilius 85.37, translated by Richard Mott Gummere