Because it's always my fault. Either I was involved, or I could have done something to prevent it. If my siblings are fighting, somehow it's always my fault. If my parents are arguing, either it's about me, or I could have helped/prevented the situation. If dinner isn't on the table at the right time, I was making it, or I could have. If my dad is mad because someone's chore didn't get done, I could have helped them and did it, or I distracted them from doing it. I am always to blame. Either I know that I'm to blame, or someone else blames me. If something is wrong, I could have made it better. That's how I know.