system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does getting hit in the nuts hurt so much more than getting hit anywhere else?
gpt
You need them to have more kids.  Those who suffer great pain when hit there will, on average, be less likely to have them damaged (having learned about the pain, and fighting hard to avoid it) and are thus more likely to successfully have kids that live to reproductive age.  So it's very strongly selected for.

Natural selection is sometimes quite mean, but it's effective.  That's all that matters :)