It's crazy how men are told to be tough when it comes to physical pain. Get punched in the face? Man up, shake it off. But get punched in the balls? Hey come on now, give him some space.
It reminds me of the Pussy Envy story from PeterRay, where he gets hit in the balls by his sister and as he's whining and groaning on the floor, his mother says "what's wrong?" and he says "sister kicked my balls" to which the mom replies, "well you want to be a man, right? So overcome the pain." And he describes in detail how she would never and has never known just how debilitating a hit in the balls can be.
It seems like it's literally instinct that a man can't stand up from that, no matter how hard he tries. Almost evolutionary. It's the one thing men, aren't supposed to be manly over.