White hair

One morning, as little Hannah was sitting at the kitchen sink watching her
mother wash and dry the breakfast plates, she noticed that her mother had
several strands of white hair mixed in with her dark hair.
Hannah looked at her mother and said, "Why have you got some white hairs,
mummy?"
Her mother replied, "Well darling, every time a daughter does something bad
to make her mother cry or unhappy, one of her mother’s hairs turns white."
Hannah thought about this information for a few moments then said, "Mummy,
so how come all of grandma's hairs are white?"