Have you ever seen someone’s arm after they have a cast taken off? Your arm hair is short because it’s being rubbed off by random interactions with things (rubbing against shirts you take off/put on, your body, general use). A person with a cast on their arm protects those hairs, and when they finally get the cast off, they look like a werewolf.
How does it know it’s short?
The follicle pooping it out is basically only gonna poop out so much before it poops out.
TIL Hair = skin excrement
Have you ever seen someone’s arm after they have a cast taken off? Your arm hair is short because it’s being rubbed off by random interactions with things (rubbing against shirts you take off/put on, your body, general use). A person with a cast on their arm protects those hairs, and when they finally get the cast off, they look like a werewolf.
It’s not a satisfying answer, but your DNA tells it.