“The rational soul is stronger than any kind of fortune — from its own share it guides its affairs here or there, and is itself the cause of a happy or miserable life.”
SENECA, MORAL LETTERS, 98.2b
You can’t count on good fortune to make you happy. It’s all luck, by definition — and anyway there’s no guarantee that it will always be good.
You can’t count on hard work either, because fortune still plays a part despite how hard you labor. You could work diligently at your job for a long time until you get promoted to be the CEO of your company… and then the company could go out of business in an economic downturn. Or disaster could strike your house or your family out of nowhere. Hard work doesn’t give you control, no matter how much we like to think it does.
What you can count on is your soul. That’s the only thing over which you truly have control. You can train your soul to be resilient and strong, no matter what fortune brings. Don’t let your soul give up before your body does.
Truly, a strong soul is the only real preparation you can make in a world that’s out of (your) control. Bad things may come and go, but if you’re resilient where it counts, they won’t overwhelm you.
A strong soul is the only real determinant of happiness in your life. Not external factors — because you can’t control those. But you can control your soul, and by training it to be strong and resilient, you can ensure your joy. Then you’ll be ready for whatever fortune throws your way, good or bad.