Basically what this is saying is that if you're looking for peace in your life, it's better to focus on changing your own thoughts, feelings, and actions rather than trying to change the people around you.
Sometimes we get caught up in wishing others were different or expecting them to change to make us happy. That doesn't really work out too well most of the time.
Instead, it's better to take a step back and look at ourselves. We can't control what other people do or how they act, but we can definitely work on ourselves.