Discussing my long hair

"You should cut it, it'll grow back thicker"
"Really, why?"
... "Because it does"
"But your hair grows because the follicle creates more hair and pushes it along. At that point the hair is dead, so how does the follicle know to create more hair? By what mechanism does this information get passed along?"
"Well everyone knows that if you cut your hair it comes back thicker"

Sigh you know at some point in our species timeline we'll stop passing on 'truths' that we have no rational basis for; knowing how the universe likes to play that point will shortly be followed by some apocalyptic event that wipes us out.

Okay longer hair is thinner at the ends than shorter hair because it wears down after time. So someone with long hair has been growing it for longer than someone with shorter hair, therefore one has thicker hair than the other because their hair is younger than the other's. If Mr. Short Hair keeps his cropped than his hair will always seem thicker than Mr. Long Hair's because it will always be younger at the tips.

The amount of hair you have is determined by the number of follicles and that isn't altered by the number of times you have your hair cut.