On Feb. 4, 2008, the eve of the U.S. Super Tuesday primaries, Sen. Hillary Clinton had an emotional moment. That’s not surprising— the business of running for president of the United States isn’t exactly a stress-free proposition. What is more surprising is the amount of attention the moment garnered: aside from presidential candidate Howard Dean’s howl four years earlier, candidates’ emotions have seldom made headlines.

But the media outcry generated when the usually controlled senator nearly had what she called “a teary moment”—when she met an old friend from Yale Law School—highlights a common double-bind professional women face: show emotion and be dismissed as incapable of leadership; don’t show emotion and be rejected as unfeminine.

“Hillary Clinton embodies women’s struggle to display professionalism without violating traditional gender role expectations,” says Nikki Graves, an assistant professor in the practice of management communication at Emory University’s Goizueta Business School.

Hitting a sweet spot between Blanche DuBois and Lady Macbeth might not sound too difficult, but Goizueta Business School scholars say it’s a huge challenge for many professional women.

The challenge, says Sherron Bienvenu, a professor emerita of management communications at Goizueta who now lives in Utah and runs an executive coaching firm, is that women and men tend to display different physical responses to changes in emotion. “Women as a group react physically when something surprises or frightens them. Men are usually more controlled, more passive,” she says. “Hillary had established herself as being very direct and controlled, so her emotional moment appeared inconsistent.”

In the workplace though, Bienvenu says, social expectations can also create difficulties. Employees commonly expect their female managers to be more nurturing than men. “There’s some expectation that a female manager is going to remember your children’s names, inquire about your weekend, and not question personal time off,” Bienvenu adds.

One study, for example, found that women managers who put candy on their desks “communicated the message that this is where the food comes from,” notes Bienvenu. This experiment may be stretching the point, she says, but it does illustrate the kind of behavior people often unconsciously expect from a female colleague. She advises young women to avoid any behavior that establishes them as the “mother” in the office.

A failure to balance expectations of being nurturing and conciliatory against a need to be perceived as tough and competent can be costly—and not just if you’re running for president. The U.S. Bureau of Labor Statistics has found that even adjusting for the time off many women take to raise their families, women still earn 5% less than men, Graves says.

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EDITOR’S NOTE: This post originally appeared here, on the Knowledge@Emory site in a best of 2010 release. The next edition of K@E is scheduled for release in mid-January. Click here to subscribe.