Warren Buffet on why even smart people get bad results, quoted by Peter Bevelin in Seeking Wisdom. From Darwin to Munger (p.36):
It’s ego. It’s greed. It’s fead. It’s mindless imitation of other people. I mean, tehre are a variety of factors that cause that horsepower fo the mind to get diminished dramatically before the output turns out. And I would say if Charlie and I have any advantage it’s not because we’re so smart, it’s because we’re rational and we very seldom let extraenous factors interfere with our thoughts. We don’t let other people’s opinion interfere with it… we try to get fearful when others get greedy. We try to get greedy when others are fearful. We try to avoid any kind of imitation of other people’s behavior. And those are the factors that cause smart people to get bad results.
I always look at IQ and talent as representing the horsepower of the motor, but then in terms of the output, the efficiency with which the motor works, depends on rationality. That’s because a lot of people start out with 400-horsepower motors and get a hundred horsepower of output. It’s way better to have a 200-horsepower motor and get it all into output. So why do smart people do things that interfere with getting the output they’re entitled to? It gets into the habits, and character and temperament, and it really gets into behaving in a rational manner. Not getting in your own way.