For every ailment under the sun
There is a remedy, or there is none;
If there be one, try to find it;
If there be none, never mind it.
Or the Serenity Prayer:
God, give us grace to accept with serenity the things that cannot be changed, courage to change the things that should be changed, and the wisdom to distinguish the one from the other.
(The meaning of the idiom that is the title of this post)