There are only two categories of things.
Things you have control over and things you do not have control over.
The things you have control over are a few. You can decide to do or not do something, you can decide what is important to you and what not, you can decide you like some things and not others. Even though it might seem you don’t, you also have control over your opinions, judgements, desires and aversions.
The things you do not have control over are quite many. For example, whether your action (or inaction) leads to a certain outcome is mostly out of our power. Also, whether others agree with you, share your same point of view, believe you are funny, beautiful, charismatic, boring, distasteful, and so. And, say the thing you like the most in the world is suddenly going to change, in shape, colour, taste, smell, packaging, quality. Yes, it is mostly out of your power.
Turns out most of the things we believe are important are in the second category. Money, success, reputation, a nice house, a beautiful family, meaningful social relationships. Sure, we can act in ways to facilitate one outcome over another, yet eventually what the outcome will be depends on factors different than our sole will.
If we turn the focus on what we have control over, instead, and close the loop there, we open to a life of satisfaction.
The point of going to the gym is not being healthy, it is going to the gym.
The point of doing good work is not getting a promotion, it is doing good work.
The point of writing is not being read, or being published, or selling millions of copies. It is writing.
And so on.