What Makes a Man a Man & a Woman a Woman?

I was recently asked the question, "What makes a man a man?", and I honestly didn't know how to answer it. In my head, certain qualities came up to describe a man, but before I spoke those words into existence, I realized that those same qualities could be attributed to a woman as well. And that's why I couldn't answer the question and felt somewhat confused and taken aback. Not because of my impulsive or knee-jerk thought, rather the fact that in that moment I truly recognized that there is no line of demarkation between what makes a man a man and a woman a woman.  I understand there are certain physical attributes that can make someone a male or female, but that's their sex, not their gender. And gender isn't black and white at all, which means that gender roles, gender identity, and gender-based qualities aren't either.