Massimo Pigliucci writes in Aeon about the power of the stoical perspective, and in particular that of Epictetus, that “if you truly understand the difference between what is and what is not under your control, and act accordingly, you will become psychologically invincible, impervious to the ups and downs of fortune.”
“For example, let’s say that you are preparing your résumé for a possible job promotion. If your goal is to get the promotion, you are setting yourself up for a possible disappointment. There is no guarantee that you will get it, because the outcome is not (entirely) under your control. Sure, you can influence it, but it also depends on a number of variables that are independent of your efforts, including possible competition from other employees, or perhaps the fact that your boss, for whatever unfathomable reason, really doesn’t like you.
That’s why your goal should be internal: if you adopt the Stoic way, you would conscientiously put together the best résumé that you can, and then mentally prepare to accept whatever outcome with equanimity, knowing that sometimes the universe will favour you, and other times it will not. What do you gain by being anxious over something you don’t control? Or angry at a result that was not your doing? You are simply adding a self-inflicted injury to the situation, compromising your happiness and serenity.”