Letters 72.4

He says: “Something will happen to hinder me.” No, not in the case of the man whose spirit, no matter what his business may be, is happy and alert. It is those who are still short of perfection whose happiness can be broken off; the joy of a wise man, on the other hand, is a woven fabric, rent by no chance happening and by no change of fortune; at all times and in all places he is at peace. For his joy depends on nothing external and looks for no boon from man or fortune. His happiness is something within himself; it would depart from his soul if it entered in from the outside; it is born there.

Seneca, Letters to Lucilius 72.4, translated by Richard Mott Gummere