why are teens and young adults that are just beginning to grow facial hair taught to shave with the mythical claim it will help things grow better?

so there is or was this claim going around since i was young and i think my dad also made this claim too back when i was a peach fuzzed teenager that for early facial hair growth, shaving it off first would improve the growth. why did people even come up with this myth? and if this ain't just a myth, then how exactly does being temporarily clean shaven improve a teen or young adult's early facial hair growth?