The Stoics had a powerful practice of rehearsing misfortune in their heads.
In this way, they were prepared for whatever happened. They could relax, and accept whatever the day brought, because they had already experienced disaster, pestilence, plague, death in the morning.
They would ask what could go wrong, and then imagine it happening. They might mentally prepare for what they’d do. They’d see that the event isn’t negative but indifferent. And then they could relax about it.
“Nothing happens to the wise man against his expectations.” – Seneca