Spend a day with any leader in any organization, and you'll quickly discover that the person you're shadowing, whatever his or her official title or formal position, is actually in sales. These leaders are often pitching customers and clients, of course. But they're also persuading employees, convincing suppliers, sweet-talking funders or cajoling a board. At the core of their exalted work is a less glamorous truth: Leaders sell.

So what kind of personality makes the best salesperson — and therefore, presumably, the most effective leader?

Most of us would say extroverts. These wonderfully gregarious folks, we like to think, have the right stuff for the role. They're at ease in social settings. They know how to strike up conversations. They don't shrink from making requests. Little wonder, then, that scholars such as Michael Mount of the University of Iowa and others have shown that hiring-managers select for this trait when assembling a sales force.