Some people are too clever to lead. Luckily, this was a handicap I was never in danger of having to overcome. Coming 247th out of 250 in a mixed ability school year group convinced me I was safe from being too smart.
As a simple rule of thumb, and for me rules have to be simple, I grade potential leaders on my four As scale. When faced with a challenge potential leaders respond with Apathy, Analysis, Answers or Action.
Apathetic responses are the hallmark of someone who will never be a leader, and probably will not be an employee for long.
The problems start with smart people who do brilliant analysis. They dazzle with their insight. They find every conceivable problem from every conceivable action. They show how any course of action is fraught with danger. They also see how the leader is always messing up. They ooze superiority and cynicism. They become energy sinks and optimism black holes.
A few bright people bring not just problems, but answers as well. This takes courage: the answer may be wrong. At least they try. They are on the road to leadership.
The true potential leader gets on with it and drives to action. They have real courage and optimism. They may not be smart enough to know the best course of action. It does not matter. When they mess up, they still have the energy to fix it and move on. These are the leaders of the future.
Finally, what of the people contrived to come below me in my year group? One has been in and out of prison, another is an investment banker and the third was the boyfriend of a (male) pop star. Life at the bottom of the barrel is at least as interesting as life at the top.