If Elon Musk is stressed, he has the option of separating himself from that stress. He works because he wants to work. Employees suffer stress from which they cannot separate themselves without, in short order, creating new stresses. Elon will not be homeless next month if he stops going to work today. A psychologist might say that his stress is therefore a product of his ego, his daily choices, rather than of his environment. It is internal to his personality. That's probably why he finds it so hard to separate.