The good news: Women at work are more capable than ever before, practically oozing competence at every turn.

Female employees now make up half the workforce, and the impact they’re having on that workforce is significant: A 2011 Catalyst analysis of Fortune 500 companies found that those businesses with women on their boards outperformed those without. There are more female entrepreneurs than ever before — the estimated 7.8 million women-owned businesses in the U.S. represent a more than 20 percent increase since 2002. More wives, for the first time in history, are out-earning their husbands.

The bad news is that women need more than competence to succeed long term. Confidence matters too, and in that area, women are coming up short. A recent study conducted for management consulting firm Bain & Company found that although 43 percent of female employees enter the workforce aspiring to top management roles, after just two years the number falls to about 16 percent. The reason for the drop off? They don’t think they can do it.

But shouldn’t competence equal confidence? Shouldn’t career success lead to stronger feelings of self worth? Some researchers look to the difference between how boys and girls are raised for explanation. Take the landmark 1980s series of studies of fifth graders by psychologist Carol Dweck, which found that bright girls were almost always the meekest in their class. The higher a girl’s IQ, Dweck found, the more likely she was to give up when a question was complex or a task was challenging. Bright girls were more easily intimidated, and quicker to doubt their ability. Bright boys, meanwhile, were more likely to see not knowing an answer — and completing a challenge anyway — as invigorating. They were not intimidated; they were naturally more confident than the girls, even though the girls performed, as a whole, better on tests. But why? Further studies over the years determined a possible reason for this: Girls, and later women, tend to believe their abilities are innate, owing to a natural talent. Boys, in contrast, believe they can make themselves better through effort and practice.

Psychologists believe this has much to do with how children are praised growing up: Girls, who are generally better behaved, are praised and rewarded for following the rules. They grow up believing that accolades are earned for who you are, more than what you do. Boys, though, are more natural rule breakers. When they receive praise, it’s more often a result of a conscious decision to act better–that is, what they do. And what they do — how they act — is, of course, changeable.

Women’s experiences confirm this. A recent report by international professional services firm KPMG found that while 86 percent of women surveyed recalled learning the importance of being nice while growing up, only 44 percent learned the importance of being a good leader. As a result, 67 percent now felt they needed to become more confident in order to take on the leadership roles they desired.

For women in the workplace, this innate tendency to underestimate themselves has been a hard habit to break. They want those top jobs, but they’re unsure they can actually do the job. Women are more easily discouraged — if a job requires a new skill, or if they’re thrust into something they believe they’re not ready for. They become too hard on themselves and conclude, too soon, that they’re “not equipped,” “not the boss type,” or “it’s not my thing.” Men, on the other hand, tend to embrace challenges as if they are simply surmountable tasks. In their 2009 book Womenomics, authors Claire Shipman and Katty Kay reported finding the same through their own research: that compared with men, women don’t consider themselves ready for promotions, predict they’ll do worse on tests, and generally underestimate their abilities. They’ll even give away the credit: A May 2013 study published in the Personality and Social Psychology Bulletin found that women in mixed-gender work teams tend to give more credit than is necessary — or even true — to their male colleagues. In some instances, women will even point to the negative aspects of themselves or their achievements instead of simply saying “thank you” or otherwise owning potential praise. The study suggested as one possible cause the rising incidence of the Imposter Syndrome, in which high-achieving people (mostly women) don’t feel they deserve the success that they have earned. And so they divert the credit onto others — namely, the men in the group.

This is the real reason that women aren’t getting ahead and staying there. Sure: Women have more to prove. They have to work longer to earn the same amount as their male counterparts and be better at their jobs to be regarded as nearly as good. But one of the biggest sources of that doubt about women’s abilities comes from women themselves. The next time you shy away from a promotion or an opportunity in favor of sticking with what you know or what you’ve been told you’re good at, reconsider. Knowing what works can be comfortable. It can also be an easy way to go nowhere. And chances are good you know far more than you think.

This article was originally published here.