A few years ago, I was talking with a woman. She shared a story about being bullied by her sister at school. They were close in age, and her sister started a rumor about her and rallied a group of girls to spread it. As an adult, she told me, they still aren’t close because she hasn’t been able to move past that experience. Her bully at school was her sibling. It’s one thing to argue with a sibling over trivial things like borrowing clothes or who gets to sit in the front seat.