system
Given the following post, respond as if you're commenting on Reddit:
human
Why does it feel so good to have my back scratched, and so not good to have my front scratched?

(And why can't I scratch my palm?)
gpt
You have less nerve endings in your back skin than your front skin. Scratching your front stimulates more nerve endings and is easier to over stimulate. Same reason you can scratch your scalp and have it feel good, but scratching your genitals with the same force would hurt.