April is Women’s History Month, and Facebook COO and Lean In founder Shery Sandberg is one of the world’s most history-making women in business today. Speaking at a panel co-hosted by Stanford Law School, Lean In, and the Hamilton Project about how women can level up in business, Sandberg said that increasing negotiation skills is one of the key ways other women can grow in business. Interestingly, what works in negotiations for men, Sandberg says, might not work for women.

Sandberg points out that success and likability are negatively correlated for women and positively correlated for men, meaning that if you’re a man who becomes more successful and powerful, you will see an increase in likability. But if you are a woman who becomes more successful and powerful, you will see a decrease in likability.

What the data says about women asserting power — by asking for a raise, for example, or by advocating for an advancement of position — is that they are often considered selfish. Words like aggressive and bossy are more likely to show up in her performance review. In the process of writing her bestselling book “Lean In”, Sandberg says she found that all over the world, the gendered stereotypes say that women should be communally focused and men should be focused on being leaders.

A product of this stereotype, Sandberg says, is that when a woman negotiates on behalf of someone else, nobody minds. She’s being communal, right? But when a woman negotiates for herself for promotions, she is more likely to be called bossy and aggressive. Sandberg makes the argument that women are less likely to be promoted at work not because they don’t ask, but because when they do ask, they’re viewed unfavorably, and the cumulative effect of this is harmful to a woman’s career.

Sandberg’s takeaway is this: If women want to get further in business, we need to get better at negotiating, and what the data says about the strongest female negotiators is that they stay focused on why giving them that raise or promotion will benefit the communal whole, not just themselves. As Sandberg says, it’s sad, but it is what is born out in the data.