really my dude...

But ok I'll entertain that like you actually have never understood the meaning of it. It means to toughen up. But because men are so archaic and mysoginistic we could not think of a better way to phrase it so we put it on an ideal that we thought we were supposed to strive to... being a man.

Since that is a negative way to view things these days, the phrase takes a beating. But anyway....
it means to toughen up.