It seems to be a philosophy about being a good little productive serf and continuing to be productive while taking your powerlessness on the nose? Why would anybody in a modern free society follow this philosophy?
As to why someone would follow the philosophy, it's simple: we all face stressful situations in life (some more stressful than others of course). Why should you let those things rule your emotions? It doesn't help anything to get upset. It just makes you feel worse. It is a pure negative thing in your life. So, you work to try to gain mastery over those feelings so that even when life is hard you can face it more effectively and with greater peace of mind.
Doesn't that seems bit pointless?
Attaching positive sentiment to the process of personal growth over percentage of success attempts allows you to build a framework of understanding to see where your sphere of influence extends to and where you can focus and continue attempting next to overcome your hurdles. You can obviously be disappointed something bad happens in relation to your efforts, but stepping back without attaching emotions to the situation allows a glimpse at the true impact of your contributions. That's part of my understanding, atleast.
If I don't accept the absurd stupidity of others, and exercise temperance and prudence in my dealings with my fellow men, life in modern society would be nearly impossible.
As an example, this very post.
Ah, don’t be too hard on yourself.