If you are like me, and I think like most people, you spend a lot of time thinking about things that have already happened.
I spend a lot of time thinking about conversations that I have had, or things that people have done. And I wonder why those things did not happen differently. I think about how I could have been better, or how someone else could have treated me with more kindness or respect. Or (and I love this one) how someone "should have known better."
We can notice those things, and notice our reactions to them. But it does not do us much good to think about how they could have been different. Perhaps they happened the way they did because they were supposed to. Perhaps they could not have happened any other way. There is no way to know this. The only thing that we can know is there is no way to go back and change anything that has already happened.
There is one change that we can make, though.
If we come across the situation again, we can remember. We can do things differently next time. This is the only thing that we can change. This is the only way that we can change.
Next time. There is nothing we can do until next time. Until then, maybe we can stop beating ourselves up about the past. Maybe we can cut our neighbor or friend or coworker a break. Maybe we can see that everyone is doing their best.