Remember this when you're thinking about something too much.
I read this in a book. The idea is that when you're thinking about something that happened recently and your mind starts getting busy and tangled up with it, take a moment and tell yourself that if you were to look at this in 1 year, would you still think about it this way? Would this even be a problem anymore? For most things, it will not be. It's just a matter of time—maybe a few hours, days, weeks, or months—and you'll completely move on from it.
For example, let's say a colleague at work replies to your message in a way that goes against your opinion or contradicts you, and you start feeling angry or overwhelmed by reading it. You begin to battle in your head about it: Why would they say that? How dare they say that? What should I reply to them? And so on. In this case, if you take a brief moment instead and ask yourself if this will still bother you in a year? Will it still be important? Will you even remember it? This trick helps you handle the problem more easily, stops you from getting angry, and makes your life happier.
The next time you find yourself in this position, use this trick to manage the situation.