It’s surprisingly simple. You learn to feel responsible for your parent’s mood.
You watch for the things that set off your parents bad moods and this abuse. Then you do everything in your power to avoid those situations happening. It could be keeping your room clean. It might be bringing your dad his drink. It might be not mentioning your shoes are too small.
not upsetting your parent becomes a part of your personality. Then you become an adult and the habit is ingrained.
it took me a very long time to get to this level of clarity. It’s a large part of why abuse makes me so angry. The children never really escape.