The error of impunity means that someone can do something wrong, but they don't get punished for it. Imagine you and your friends are playing a game where you can't touch the ground. But one of your friends accidentally touches the ground and the other friends don't say anything about it. That's kind of like the error of impunity. It's when somebody does something wrong, but they don't get in trouble for it. It's important that people are held responsible for their actions, just like how you would be held responsible if you broke your mom's vase even if it was an accident.