system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why male human testicles are so venerable / sensitive, considering their importance?

I mean you think evolution would have created an armour casing for them or kept them inside the body for protection?
gpt
The male testicles in humans are vulnerable because they are external to the body really and unprotected by body fat bones etc. But why should this be? Sperm happen to be very temperature sensitive and they seem to thrive when the temperature is slightly lower than they would be if they were internal. By having them in the scrotum which contracts and stretches if it's cold or hot respectively temperature can be controlled rather tightly to make sure they are always in prime condition (we think even weekly warm baths actually reduce sperm quaility as do tight underwear/pants when their temperature regulation is hindered!)

But then why not make them insensitive to pain? Well they are vital to our existence without them we can't procreate so they are sensitive as this makes men take care of them.