The principles of Stoicism are easy to put into practice when stuff’s going well. To express gratitude for what you have, to aim for tranquility to be your core emotion, and that you only control what you do and you have ZERO control over what others do.
But it’s when things are turbulent that they’re put most to the test. When you’re at your most vulnerable, you need the calming effect to ease the impact of the waves pounding at the ship. Stoic principles (and you inner strength) is most tested in those times, which is when you need them the most.