A good manager will hire smart and able people, who will naturally gravitate to him. He's not intimidated by people smarter than himself.
A poor manager not only will not, but cannot surround himself with good people. He wouldn't know a good employee if he saw one, would probably find be repulsed by somebody smarter than himself, and good people tend to stay away from fools.
Yup. And also, the second a good manager lets his guard down and hires an idiot, the whole thing collapses rapidly. That one idiot destroys the cohesion, the morale and the desire to excel in the rest.
Oh did I get an inside view on that one once.