Keith Stanovich, aprofessor of psychology, likes to distinguish between intelligence quotient (IQ), which measures mentalskills that are real and helpful in cognitive tasks, and rationality quotient (RQ), the ability to make gooddecisions. His claim is that the overlap between these abilities is much lower than most people think.

The physicist and science writer Leonard Mlodinow puts the point more broadly. “While IQ scores may correlate to cognitive ability,” he writes in Emotional: How Feelings Shape Our Thinking, “control over and knowledge of one’s emotional state is what is most important for professional and personal success.”