Career women face a double bind: the more competent and assertive they are, the less liked they are (these traits are positively correlated with likability for men, negatively for women), and reduced likability makes women less effective as leaders . If they are not very assertive, they may be  well-liked but they are not perceived as very competent, so their effectiveness suffers again. So damned if you do, damned if you don’t. 

For the geeky among us, here’s a handy illustrated guide to women’s careers.