You can't control what happens to you, only your reaction to it.
Marcus Aurelius was a Roman emperor, and one of the great Stoic thinkers.
One of the key tenets he lived by was that we are not in control of our existence, only the universe is. Whatever the universe hands us, we must accept, as the universe is good.
He puts forward the idea that our reactions to things that happen to us is where we display true freedom.
This freedom means we can choose and mediate our reactions to whatever happens to us, rather than being a slave to our emotions.
While I may disagree that we live in an unchangeable world that we cannot bend to our will, the idea of controlling our reactions is the thing we should focus on really does resonate.
The next time someone cuts me off in traffic, or is actively unpleasant, my reaction is my own. Nobody can control that except me.
That brings to question another one of Aurelius' teachings, that when someone does something to harm you, if you choose not to be harmed, you haven't been. It says more about their inability to control their actions than it says anything about you.
This reminds me of Hanlon's razor.
Never attribute to malice that which is adequately explained by stupidity.
Other people are never going to be faultless, and neither are you.
But if you're working on controlling your emotions and your reactions, that's the most you can do.