Store managers and psychologists have long believed that outgoing individuals make the best salespeople. Yet research now suggests that extroverts are actually less successful at making sales than people with more moderate social temperaments. Adam Grant, associate professor of management at the Wharton School of the University of Pennsylvania, gave personality tests to 340 salespeople and compared their extroversion scores to their yearly revenue. Those who scored exactly halfway between the poles of extreme extroversion and extreme introversion—whom Grant calls “ambiverts”—earned 24 percent more than the introverts and, surprisingly, 32 percent more than the extroverts.

Grant—who is a self-described ambivert and a former salesman himself—says he is not sure why such individuals perform better, but it may be that “they're less likely to get distracted and to talk too much—they find the right balance between talking and listening.” In addition, extroverted salespeople may sometimes be too pushy and turn potential buyers off.

Next, Grant plans to investigate whether successful ambiverts are always socially even-keeled or whether they tend to fluctuate between extroversion and introversion depending on factors such as mood or the temperament of their customers.