There was a girl brought up a servant in a castle, subject to the whims of her kind-enough but autocratic mistress.
She was called lazy and clumsy so many times she believed it.
When it turned out she was actually the legitimate ruler of the kingdom, and was placed on the throne, her laziness and clumsiness made her a very bad ruler; her reign lasted only until someone ‘accidentally’ shot her with a crossbow.
The moral of the story: we truly are what we believe we are, and it’s very hard to change.
Be careful what you tell children.