From the Buddhist tradition: if something can be done about it, what need is there for dejection? If nothing can be done about it, what use is there for being dejected….
(Note: dejection means a sad or repressed state, a lowness of spirit)
And from the Christian tradition: God give us the grace to accept with serenity the things that cannot be changed, the courage to change the things which should be changed and the wisdom to know the difference...