I don't know if you are trolling, but it is high risk because yahoo is a company that is incredibly difficult to turn around. Meanwhile, Apple is already very successful, so you "just" need to keep it moving.
It is not high risk in the sense that you might go broke working as the ceo.
On the contrary he had huge shoes to fill, expectations to match and momentum to carry. Success is not an accident. You can always lose momentum, you can always make the wrong decisions, you can always fail, especially in a company as keenly watched as Apple, holding on to leadership in categories it created, with the pressure of innovation in a hyper competitive industry. Look at Nokia.
It is not high risk in the sense that you might go broke working as the ceo.