Ridiculous Things Mom and Dad Made Us Believe 

In werewolf culture, it is believed that their powers activate at the arrival of the full moon. Their mother, who was a fan of vampire and werewolf trilogies, convinced their kids for fun that cutting their hair in the full moon would make it grow longer at a faster rate.

Each month when the full moon arrived, her kids grabbed the scissors and gave each other haircuts. The psychology that their mother instilled into their heads made them believe that it was working, until they grew up and realized that there is no way hair growth has anything to do with the moon.