Letters 103.3

You must, however, reflect thus what danger you run at the hands of man, in order that you may deduce what is the duty of man. Try, in your dealings with others, to harm not, in order that you be not harmed. You should rejoice with all in their joys and sympathize with them in their troubles, remembering what you should offer and what you should withhold.

Seneca, Letters to Lucilius 103.3, translated by Richard Mott Gummere