This appears to be shoehorning in something other than the trope: it's not a case of a powerful character forgetting they get to set the rules.
The case of the whipping boy. In order to teach spoiled princes to behave, they had to be punished when they did wrong. However, it is a crime for anyone to lay their hands on the prince. Therefore (and here is royal logic at it's finest) they take a peasant boy from somewhere, and make him the whipping boy, punishing HIM whenever the prince does wrong. Now, if they were a good kid, the idea of someone else getting hurt every time they misbehaved would make you behave. However, the kind of prince that needs a whipping boy isn't going to care. What should have been a lesson teaching that others suffer if you do wrong, instead teaches that you'll never suffer the consequences of your actions.
This appears to be shoehorning in something other than the trope: it's not a case of a powerful character forgetting they get to set the rules.