Where did the generalization come from that women are hard to understand?

You’ve heard the stereotypes. Is it just me? Or does it seem like there’s a stereotype that women are an enigma that is not to be questioned because we’ll never understand anyway? Like we’ve tried so hard for centuries to find out what women want and how they think, but have only failed and it has become a social norm to just take it at face value.

This is just about the generalization, I’m not discussing if women (in general) are actually this way (from my observation, I don’t think it much true, anyway). We all know how lame stereotypes are. I was just curious, because it’s one I was unfamiliar with, and even though damaging, they’re still interesting.