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(CNN) -- In 2000, only 11.7 percent of Fortune 500's board members were women. Today, that figure is still disappointingly low at just 16.9 percent.
Heather McGregor, a former investment banker turned headhunter, thinks she might know why this is.
As managing director and principal shareholder of the executive search company Taylor Bennett, she recently wrote "Mrs Moneypenny's Careers Advice for Ambitious Women."
Speaking at this year's Names not Numbers conference, an event where CNN International was a media partner, McGregor explains that the sooner women accept that they can't have it all, the better.
"The biggest challenge to women in the workplace that still hasn't changed is the level of unconscious bias. So people have in their minds that they would prefer not to hire or promote a woman and they don't even realize that they feel like that.
I know as a headhunter that if I propose two candidates of equal skills, maybe they're both in their mid thirties, one's a man and one's a woman, and the woman has recently gotten married, assuming there's nothing else to choose between them, the employer will choose the man and that's even if the employer is a woman."
"The best careers advice I've ever received myself, which was so good that I wrote a whole book based on it, is that the way we can smash the myth of the glass ceiling is to smash the myth that women can have it all. To really pursue a career is no different to pursuing your gold medal in the Olympics.
You have to make choices and they're not always easy. In my experience, if you try and do everything well what will end up happening is you will end up disappointing everyone. Much better to disappoint a very small number of people and everybody else is not disappointed, and furthermore supportive of you and your career."
"People still think that women are not going to be as reliable a hire as a man, especially in those mid years. It's a sad truth today, and I hope this will change, that women have to not just be as good as a man, but better.
Because if you're faced with two people and one of them is a 35-year old woman with a wedding ring, and she's noticeably better than the man, you'll still hire the 35-year-old woman with a wedding ring."