Conditional control
If something is out of your control, all you can do is change how you react. But if it’s in your control, you can change how you act. Sounds simple, but I wonder how much distress comes from not applying this simple rule (a conditional heuristic). It’s common to (a) accept your initial reaction without realizing you can change it, (b) get worked up over things you can’t change, (c) justify a reaction to avoid taking action, because of fear, and (d) take delusional action towards something that is entirely unrealistic. This saying solves all four.
Another way to think about it: people don’t act on this because of mislabeling, avoidance, or incompetence. They either can’t measure their agency (they mislabel if they can control it ), don’t want to accept the conclusion (they want to avoid helplessness or meaninglessness), or don’t know the techniques of habit change or mindset change.