“The chief task in life is simply this: to identify and separate matters so that I can say clearly to myself which are externals not under my control, and which have to do with the choices I actually control. Where then do I look for good and evil? Not to uncontrollable externals, but within myself to the choices that are my own.”
— Discourses, 2.4.4–5
Or, as we Christians say:
I like the complete Serenity Prayer:
God, grant me the serenity
to accept the things
I cannot change,
Courage to change the
things I can, and the
wisdom to know the difference.
Living one day at a time;
Enjoying one moment at a time;
Accepting hardship as the
pathway to peace.
Taking, as He did, this
sinful world as it is,
not as I would have it.
Trusting that He will make
all things right if I
surrender to His Will;
That I may be reasonably happy
in this life, and supremely
happy with Him forever in
the next.
Amen
Reinhold Niebuhr (1926)
