I used to stress about things that were out of my control all the time. To some extent, I still do.
It used to be really bad in the past, to the point where I just couldn't stop thinking about things, and could not let them go. It would negatively impact my life in many ways.
I think that I managed to slowly get more control over myself and my mind, so I am much better at letting things go, which means that I don't think about things obsessively or let them take control of my life by completely stressing me out.
Of course, its not perfect now, there are still times where I find myself stuck in a sort of loop of thoughts about things that happened or that I fear will happen, or that I want to be different. These things may sometimes not have anything to do with me, but I will still have them stuck on my mind.
Sometimes I can let these thoughts go by stopping and taking some deep breaths, other times though this doesn't work, and I need some sort of distraction to take my mind of things.