Enchiridion 14

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.

Epictetus, Enchiridion 14, translated by W. A. Oldfather

If you would have your children and your wife and your friends to live for ever, you are silly; for you would have the things which are not in your power to be in your power, and the things which belong to others to be yours. So if you would have your slave to be free from faults, you are a fool; for you would have badness not to be badness, but something else. But if you wish not to fail in your desires, you are able to do that. Practise then this which you are able to do. He is the master of every man who has the power over the things, which another person wishes or does not wish, the power to confer them on him or to take them away. Whoever then wishes to be free, let him neither wish for any thing nor avoid anything which depends on others: if he does not observe this rule, he must be a slave.

Epictetus, Enchiridion 14, translated by George Long

It is silly to want your children and your wife and your friends to live for ever, for that means that you want what is not in your control to be in your control, and what is not your own to be yours. In the same way if you want your servant to make no mistakes, you are a fool, for you want vice not to be vice but something different. But if you want not to be disappointed in your will to get, you can attain to that.

Exercise yourself then in what lies in your power. Each man's master is the man who has authority over what he wishes or does not wish, to secure the one or to take away the other. Let him then who wishes to be free not wish for anything or avoid anything that depends on others; or else he is bound to be a slave.

Epictetus, Enchiridion 14, translated by P. E. Matheson