I’ve read and reread this book.
The writer mentions is that all our upsets involve us adding something to the situation where we are upset. In this case, upset refers to any degree of negative emotionality, including slight annoyance.
What do we add that causes the upset?
I am not going to tell you.
If you are upset by this , ask yourself what you are adding to the situation?
If you are not upset, what would you have to add to the situation to be upset?