Your mum had to pop next door for twenty minutes and left you in charge of your younger sister. "Just keep an eye on her," she said. The moment the door closed, your sister announced she doesn't have to listen to you because you're "not the boss of her." She wants to do something you're pretty sure isn't allowed — climbing on the kitchen counter to reach the biscuits. You tell her no. She does it anyway, grinning at you. You don't actually have any power here, and you both know it. But you're the one who'll be in trouble if something goes wrong.