[viscanti]

Obviously you're taking things to an extreme (but understandable, given the initial remark you're responding to) degree. A better wording would have said something like "A CEO should know a little (or a lot) about all the c-level roles". These are the people they'll need to work with and delegate to.

Tim Cook wouldn't benefit from a more thorough understanding of the janitor's role. He would benefit from understanding operations, marketing, finance and technology. His ultimate responsibility is to recruit and retain the best people for those roles. He doesn't need to be world-class at each, but he needs to be able to identify what world-class looks like for each c-level role.