system
Given the following post, respond as if you're commenting on Reddit:
human
Why are the undersides of our nails rough?

When you clip your nails, the underside is extremely rough, almost like sandpaper. The top however, is smooth. I was under the impression that the nails exist because of the sensitive skin, so wouldn't this rough texture irritate it more?
gpt
Your nails are "built" that way on both sides, but during the months of time it takes for the nail to grow out, the top is constantly exposed, and essentially gets sanded down. 

The bottom is not, and is essentially adhered to the skin underneath the whole time.