The CEO of an Ambulance company I know has about 500 staff, he's been doing it for 25 years, it all seems like a smooth operation but they're constantly facing issues. Labour and training problems, international actors that won't pay and their governments won't help, shipping problems, supply chain problems. Liability issues. IP issues with some special things they do. Orders come in batches, they might have a down year and possibly have to play people off. And I'm not even getting into the very basics of product development, financing the working capital i.e. the regular stuff employees do.
People who think CEO's just show up and wear suits and have meetings, and kiss up to the board ... I don't think have any exposure to what the job entails.
Again, that's not hard as in big "physical or mental toll". Being a miner is hard. Being a surgeon is hard. Being a mathematician working on big problems is hard.
A CEO compared is a walk in the park. All those issues you've mentioned ("Labour and training problems, international actors that won't pay and their governments won't help, shipping problems, supply chain problems") are there in any business (even in a single person shop).
That makes it volatile, not hard. And the stakes are much less for volatility when you already have several cool million in the bank...