Two things you won’t fret over if you’re a wise man; the thing you can’t help, and the thing that you can. (Dictionary of English Proverbs/Thomas Preston)
Worry that increases anxiety may be the result of focusing on things you either can’t do anything about or those things you can (but won’t) do anything about. Another way of say the same thing is the Serenity Prayer by Reinhold Neibuhr.
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.
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.