Warren Buffett often declares that, to succeed, more important than IQ, is rationality and emotional stability. Morgan Housel discusses:

Take two investors. One is an MIT rocket scientist who aced his SATs and can recite pi out to 50 decimal places. He trades several times a week, tapping his intellect in an attempt to outsmart the market by jumping in and out when he’s determined it’s right. The other is a country bumpkin who didn’t attend college. He saves and invests every month in a low-cost index fund come hell or high water. He doesn’t care about beating the market. He just wants it to be his faithful companion. Who’s going to do better in the long run? I’d bet on the latter all day long. “Investing is not a game where the guy with the 160 IQ beats the guy with a 130 IQ,” Warren Buffett says. Successful investors know their limitations, keep cool, and act with discipline. You can’t measure that.