The duty of a man is to be useful to men: to a great number if he can, if not, to a small number, otherwise to his neighbors, otherwise to himself: in making himself useful to himself, he works for others. Also the vicious man injures not only himself but also those to whom he might have been useful if he had been virtuous, likewise in laboring for oneself one labors also for others, since there is formed a man who can be of use to them.
Seneca (Roman Stoic philosopher, statesman and dramatist)