"We have no Master, no Whips, no House of Pain any more. There is an end. We love the Law, and will keep it; but there is no pain, no Master, […]." (21.10)
So deeply ingrained are the rules that even after the threat of punishment has passed, the rules still stick. It's even worse when it's your mother's rule—you can still hear her disappointed voice in the back of your head when you mess up as an adult. Seriously, those are the worst.