one so important that Epictetus called

The first hurdle – one so important that Epictetus called it "our chief task in life" – is to identify what is outside of your control to begin with, aspects the Stoics call "externals". Luckily, the Stoics made this rather simple: it's everything other than your own thoughts, choices and actions. Take health, for example. You may choose to eat five-a-day and exercise (your choices), but that doesn't mean you won't ever suffer any health issues (an external). And if you think it does, you're not just deluding yourself. You're setting yourself up for real disappointment.