Life is short, don't sweat the things outside your circle of influence.
One of my manager's at Disney said those words to us one day, and the comment, as well as the meaning has stuck with me all these years. There's so many things in life that affect our feelings and actions but if you can't change it, let it go. It's not worth your health and happiness to worry about a comet that might hit earth, or the injustice of a person getting off for a murder you are certain they committed. Life has a way of working it all out in the end, at least that's what I believe. Karma is a powerful unseen force.