It's not IQ. The big thing is rationality. I always look at IQ and talent as representing the horsepower of the motor, but that the output – the efficiency with which that motor works – depends on rationality. A lot of people start out with 400-horsepower motors but only 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 habits and character and temperament, and behaving in a rational manner. — Warren Buffett (Source: Tap Dancing to Work by Carol J. Loomis, P.134)
While many people assume that intelligence and rationality are related, Stanovich shows that these are distinct abilities. This is why we see objectively intelligent people make poor decisions…He argues that plenty of people have adequate intelligence but an inability to think and behave rationally…Conversely, you don't need the IQ of a genius to make good decisions. — Keith Stanovich (Source: The Success Equation by Michael J. Mauboussin)