Honestly, being spanked once had, like, zero effect on me. It was watching all the shut with my sister that made me desperate to just blend into the woodwork, in part because I could see my parents were already overwhelmed and in part because my sister enjoyed targeting me when she needed a punching bag.

My parents were overwhelmed and terrified by my sister's behavior and their methods of dealing with it were wildly inconsistent. Sometimes it was therapy, sometimes appeasement, and sometimes yelling/spanking. I have no idea what would have worked and sadly, neither did they.