Why does it feel good when your back is scratched?!
Question:
Why does it feel good when your back is scratched?
Is it the mere human closeness, or does it serve a function?
Answers:
When done by someone else, you personally have no idea what pattern or route the hand and nails is going to take, so it's always a suprise, thus it feels good.
When you do it yourself, there is no element of suprise. Subliminally, your itch sends a request to the brain, the brain instructs the nails and the nails take care of the itch.
Itch gets scratched, but it was all pre-planned.