Sheryl Sandberg, the Chief Operating Officer of Facebook, is the first woman to become a social-media billionaire. An incredible accomplishment highlighted in TIME Magazine’s Firsts Edition on Women changing the World.

“The world accepted that girls didn’t really do math contests.”

was a nerd. When I was in high school, I went to a math competition because my math teacher told me to. I liked it and I did fairly well, but there were no other girls. Even though my parents encouraged me to do anything, I came back and said to my math teacher, “Girls don’t do this.” He said, “You’re right.”

He was an amazing man and he really pushed me in math, but a better answer would have been, “And that’s why you should do it!” But the world accepted that girls didn’t really do math contests. We systematically treat girls and boys differently from birth—boys get paid more allowance as kids and do fewer chores, for example. Any woman in the workplace will recognize that pattern: we do more work and we get paid less.

We suffer from the tyranny of low expectations when it comes to women and equality. I remember in 2012, when women won 20% of the seats in the U.S. Senate. Fifty percent of the population, but 20% of the seats. All the headlines screamed, “Women take over the Senate, women take over the Senate!” Fifty percent of the population with 20% of the seats is not a takeover—it’s a gap. Now, we should celebrate every Senate seat a woman takes, but the goal is equal representation. This is true in all industries. We should have half the leadership roles, and we’re very far from that. But we will get there.

I came into the workforce in 1991. I looked beside me: equal men and women. The women were just as smart, sometimes smarter (no offense, gentlemen). I looked above me, and it was men. I figured, O.K., that’s historical discrimination. My generation will change it. But as the years went on, there were fewer and fewer women in the meetings I was in. This stalling of progress for women in leadership led to my writing Lean In. Women had moved forward from the ’60s or ’70s till about 10 years ago, and they have stopped. We need to fix that, be alarmed by that, proclaim it as the really urgent crisis it is.

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