What is "ならぬことはならぬものです"？

In Aizu domain, Children from 6th to 9th gathered to form a group of 10 members, and the most senior one was in charge of the group to educate the rules. When they turn in 10, they were supposed to go to school run by Aizu-han, and this group formation and the lecture was a very crucial preparation before becoming a student. Here is the list of the rules.

• Never oppose what your seniors say.

• Always make a bow to your seniors.

• Never play unfairly

• Never pick on people smaller than you.

• Never eat outside of your house

• Never speak to ladies outside of your house

At the end of these rules, there were always a phrase “What you must not do, you must not do”. Every week the group gathered one member’s house and the leader ask if there was anyone who had broken the rule. This is how people in Aizu domain earned the sense of obligation and morality even in their very early period of their life.