Psychologically Invincible

Epictetus’ promise: if you truly understand the difference between what is and what is not under your control, and act accordingly, you will become psychologically invincible, impervious to the ups and downs of fortune.

God, grant me the serenity to accept the things I cannot change,
Courage to change the things I can,
And wisdom to know the difference.

-Reinhold Niebuhr, circa 1934

The sentiment behind the prayer is very old, found in 8th-century Buddhist manuscripts, as well as in 11th-century Jewish philosophy. The oldest version I can think of, however, goes back to the Stoic philosopher Epictetus. Active in the 2nd century in Rome and then Nicopolis, in western Greece, Epictetus argued that:

We are responsible for some things, while there are others for which we cannot be held responsible. The former include our judgment, our impulse, our desire, aversion and our mental faculties in general; the latter include the body, material possessions, our reputation, status – in a word, anything not in our power to control. … [I]f you have the right idea about what really belongs to you and what does not, you will never be subject to force or hindrance, you will never blame or criticise anyone, and everything you do will be done willingly. You won’t have a single rival, no one to hurt you, because you will be proof against harm of any kind.

Full article:

https://aeon.co/ideas/to-be-happier-focus-on-whats-within-your-control

‘To Be Happier, Focus On What’s in Your Control’

by Massimo Pigliucci and edited by Nigel Warburton, AEON