This is something that I remember hanging on a little card on my grandmother's wall next to her door when I was a child. I never asked her about it, but I think it must have brought her peace after my grandfather passed away. I have used it many, many times in my life to gain some perspective on the things that are too big for my plate. Repeating this works for me and brings me a sense of grace and peace. If you're struggling yourself with something, it's a good way to meditate on it for a bit, maybe it will work for you, too.
God, grant me the serenity
to accept the things I can not change,
courage to change the things I can,
and the wisdom to know the difference.
Peace to you today in whatever struggle you may face,