The fundamental cause of emotional pain is resisting reality ~ Hal Elrod
This goes right along with the idea that you can only be hurt by things that (you believe) have truth in them.
Pause, breathe, and say to yourself "can't change this". Then examine yourself to see if it TRULY IS something you have no power to change.
If yes, then move on with your day, because fretting about something that only someone else can change won't bring about the desired change. It only clogs up your brain space.
If it's something you DO have the power to change, or at least influence, then determine what action you can take to affect the change, implement it, and move on.
I'm both instances you will have an much improved mindset for the day.
More importantly, you will have proved to yourself that you have the power to choose your mindset (feelings) towards any situation you come up against.