How could Tim Cook be chosen by Jobs as his successor?

Apple version of the two whatevers: what Mr. Joe says is what we do. "Tim Cook is the best employee I have ever recruited."-Joe Wang Jinkou Yu Yan, Apple version of "You do things, I feel at ease". Here Jobs refers to his operational ability, workaholism, low profile, not stealing the boss's limelight and so on. Maybe Mr. Joe also said, "If you have any questions, ask Scott", but that doesn't matter anymore.