Women comprise today more than half of the talent pipeline (holding some 60 percent of graduate degrees), and the majority (64 percent of senior women, according to Center for Talent Innovation research) are eager to be promoted to the next job level.

Yet we also find that, at the door to the C-suite, they hesitate to cross the threshold -- fearful, we suspect, of having to walk the tightrope between feminine and authoritative, and between effective and likable. Men simply aren’t forced to choose, since by dint of being male they’re already perceived as leadership material.

Since the early 1970s, when social scientist Virginia Schein showed that both male and female managers perceive leadership attributes as more likely to be held by men than women, studies have repeatedly confirmed that we associate masculine attributes with leadership suitability and feminine attributes with serve-ability -- “taking charge” skills being the province of men, and “taking care” skills being the province of women.

Related: Stop Fixing Women to Act Like Men

Women perceived as having certain traits. Despite research showing that gender is not a reliable predictor of how a person will lead, we persist in vetting leadership candidates on precisely that basis. Women are seen to embody such “feminine” traits as being less self-confident, less analytical and less emotionally stable, traits not associated with capable leaders; whereas traits we associate with being masculine -- being aggressive, dominant, objective, and competitive -- are considered requisite to leadership. Compounding this stereotypical perception of women is men’s inability to perceive their own “invisible knapsack” of privilege, that kit of inborn traits that grants them access, acceptance and authority they’re unaware they’re carrying.

When women do manifest the requisite traits, we’re inclined to punish them for it. Experiments repeatedly surface our inclination to fault women for career ambition and entrepreneurial smarts while rewarding it in men.

In an experiment conducted at the Stern School of Business at New York University in 2003, male and female graduate students who assessed the leadership capabilities of a real-life successful entrepreneur named Heidi were far more inclined to admire this accomplished individual when she was recast as Howard.

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Judging the likeability factor. Students given the case study about Heidi perceived her as “selfish,” “out for herself,” and “a little political” -- in short, not as likable as Howard. When this experiment was replayed in 2013, substituting Kathryn and Martin for Heidi and Howard, students actually liked Kathryn slightly better than Martin (8 versus 7.6) -- but they didn’t trust her nearly as much (6.4 for Kathryn, 7.8 for Martin). As the evaluators explained to CNN correspondent Anderson Cooper, who staged the replay, “men seem more genuine,” whereas women seem to be “trying too hard,” making them less trustworthy.

The likability-versus-competence tradeoff is arguably the most tenacious, as well as pernicious, double bind that women in leadership confront. First documented in 2004, when Madeline Heilman and others found that successful women, unlike successful men, suffered social rejection and personal derogation (especially when their success was in a male-dominated arena), it continues to be corroborated.

A large-scale study of 60,470 men and women conducted in 2011 found that, while slightly more than half (54 percent) of participants said they had no preference when it came to choosing the gender of their boss, the other 46 percent indicated a strong preference for a male superior -- by more than a 2-to-1 ratio, in fact.

Those who said they preferred a male boss cited not the positive attributes of male leaders but rather, the negative attributes of female leaders. Comments such as “catty” or “bitchy” cropped up a lot in these discussions. “While not directly addressing the competence of female leaders, these comments attach the personality of the female leader, indicating that some perceive these abstract female leaders as less likeable than men,” the researchers observed.

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The tradeoff. Every time a woman takes the national or international stage, the likability/effectiveness double bind surfaces. Feminist blogger Jessica Valenti, writing for the Nation, noted that “women adjust their behavior to be likeable and as a result have less power in the world” -- an acceptable tradeoff, to her way of thinking, but nonetheless a tradeoff.

Most recently, Sheryl Sandberg, Facebook’s No. 2, has observed the tradeoff and lamented its impact on potentially high-impact women. “I believe this bias is at the very core of why women hold themselves back,” she wrote in her 2013 take-charge manifesto, Lean In. “It is also at the very core of why women are held back.”   

Reprinted with permission from Executive Presence by Sylvia Hewlett. Copyright 2014. HarperBusiness, a division of HarperCollinsPublishers.   

Related: Women Win in the Classroom, Struggle in the Boardroom (Infographic)