Chances are it might be your only regret, too.

By Liz Steelman
Updated September 07, 2017
The Washington Post/Getty Images

Sandberg’s interview is part of TIME Firsts, a multimedia project featuring 46 groundbreaking women. Watch the rest of the videos at Buy the book at the TIME Shop.

Not reading Crime and Punishment when it was assigned, hanging out with the wrong crowd, spreading yourself too thin across activities. Whatever your high school regret is—we all have them. Even, remarkably, Sheryl Sandberg. Yes, even the chief operating officer of Facebook and bestselling author of Lean In has moments she wishes she could do over.

For Sandberg, her biggest high school regret was not participating in math competitions because she would have been the only girl. She recalls approaching the math teacher to tell him this in a trailer for Firsts, TIME magazine’s newest multimedia project featuring 46 groundbreaking women. Rather than pushing back, he wholly accepted her reasoning.

“The better answer should have been, ‘And that’s why you should do it!’” Sandberg says in the video. “But there were no girls, and the world accepted that girls didn’t really do math competitions.”

This was Sandberg’s formative brush with what she calls the “tyranny of low-expectation.” Instead of pushing women to participate farther and longer than they are expected, the world accepts when they admit defeat, even when a fix is possible or accommodations can be made to help them along. And though the experience is a sore spot, she’s devoted a large part of her career to helping women fight back against it.