"Of all the means which wisdom acquires to ensure happiness throughout the whole of life, by far the most important is friendship." - Epicurus
We only have control over ourselves. If you think you can control others you’re only going to make your life and others lives unpleasant. Some things are easier to accept than other things, if someone has different taste in music to you, that’s easy to accept. A different political opinion, well… lets just not talk about it, we can still be friends. What if someone says they’re going to do something for you but they don’t? How aggravating. They’ve let you down.
Something I’ve read a lot of lately is just accepting that things are the way they are. Stuck in traffic? What are you going to do, be angry or just accept that this is the way things are right now? You’ve got no choice if you want to be happy. Someone doesn’t meet your expectations? Exactly, they haven’t met your expectations. There is no point in being angry, let others be and you can be too. Your view of the world is totally self-imposed. If you want to see the colour green all day long, you probably could if you tried, it’s up to you.
Not being able to accept things can make you angry, or sad, both are just as pointless in the end. Both defeat happiness if you let them.