Adichie argues that the definition of masculinity is narrow—that it's "a hard, small cage, and we put boys inside this cage." Her idea here stems from how boys are raised. While we teach women to be soft and "likable," we teach boys to fear emotion and vulnerability. As a society, we are teaching boys to be "hard" men and to mask their true identities. We put them in an emotional box, stating they cannot stray from this invisible barrier. They must not feel too deeply, or they cannot be considered men.
Adichie backs up this claim by talking about societal roles and how even today, men are still expected to be the breadwinner and pay for things. One example in this section of her talk is the connection to money. If we can teach boys that money does not equal being a man, maybe their perceptions of the world would shift, allowing women to step in and be on a new level of success in the workplace without being called "aggressive."
We teach men that they are superior, and because we don't allow boys to feel and step into their authentic selves, we end up creating fragile egos in these boys who are now unable to handle their emotions and the world around them. As for the girls, we teach them to cater to these weak egos which reinforce the glass ceiling they are so desperately trying to break through.
Her solution is to raise our boys differently, allowing them to grow into whoever they want to be without archaic gender constraints and oppressive social contracts. Boys will not change unless we allow them to, so we all need to be feminists, step in, and create the shift.