If you make it your will that your children and your wife and your friends should live for ever, you are silly; for you are making it your will that things not under your control should be under your control, and that what is not your own should be your own. In the same way, too, if you make it your will that your slave-boy be free from faults, you are a fool; for you are making it your will that vice be not vice, but something else. If, however, it is your will not to fail in what you desire, this is in your power. Wherefore, exercise yourself in that which is in your power. Each man’s master is the person who has the authority over what the man wishes or does not wish, so as to secure it, or take it away. Whoever, therefore, wants to be free, let him neither wish for anything, nor avoid anything, that is under the control of others; or else he is necessarily a slave.