You often hear this in relation to debates about economic inequality. For example, feminists bemoan the lack of female CEOs, saying that women can be just as tough, ambitious and decisive as men.
Much of this is laudable, of course. It's also true, because there are many aspects of male and female psychology that hardly differ at all. But it can cause a lot of confusion and frustration as well -- particularly in intimate relationships. This is because whether we like it or not, men and women are also very different in so many ways -- often ones that are unchangeable.
Take the issue of a potential partner's relative height. Both men and women prefer it if the man is taller than the woman. And it seems that this requirement is more important for women than it is for men.
Here's an interesting and comprehensive post on this particular phenomenon.