You've undoubtedly heard of Saint Francis of Assisi (Giovanni Francesco di Bernardone; 1181/1182 – October 3, 1226, and the serenity prayer attributed to him, but modern scholars give credit for the prayer to Reinhold Niebuhr who wrote it for use in a sermon, perhaps as early as 1934.

God, grant us the... Serenity to accept things we cannot change, Courage to change the things we can, and the Wisdom to know the difference Patience for the things that take time Appreciation for all that we have, and Tolerance for those with different struggles Freedom to live beyond the limitations of our past ways, the Ability to feel your love for us and our love for each other and the Strength to get up and try again even when we feel it is hopeless.

But as is often true the ideas have a much earlier origin, at least as far back as Epicitus, who in my opinion said it much better.

The following is from The Encheiridion (The Handbook) compiled by a student of Epictetus at the beginning of the 2nd century. Epictetus was a stoic.

Some things are in our control and others not. Things in our control are opinion, pursuit, desire, aversion, and, in a word, whatever are our own actions. Things not in our control are body, property, reputation, command, and, in one word, whatever are not our own actions.

The things in our control are by nature free, unrestrained, unhindered; but those not in our control are weak, slavish, restrained, belonging to others. Remember, then, that if you suppose that things which are slavish by nature are also free, and that what belongs to others is your own, then you will be hindered. You will lament, you will be disturbed, and you will find fault both with gods and men. But if you suppose that only to be your own which is your own, and what belongs to others such as it really is, then no one will ever compel you or restrain you. Further, you will find fault with no one or accuse no one. You will do nothing against your will. No one will hurt you, you will have no enemies, and you not be harmed.

Aiming therefore at such great things, remember that you must not allow yourself to be carried, even with a slight tendency, towards the attainment of lesser things. Instead, you must entirely quit some things and for the present postpone the rest. But if you would both have these great things, along with power and riches, then you will not gain even the latter, because you aim at the former too: but you will absolutely fail of the former, by which alone happiness and freedom are achieved.

Work, therefore to be able to say to every harsh appearance, "You are but an appearance, and not absolutely the thing you appear to be." And then examine it by those rules which you have, and first, and chiefly, by this: whether it concerns the things which are in our own control, or those which are not; and, if it concerns anything not in our control, be prepared to say that it is nothing to you.