If you get detention Monday for not eating peaches, Tuesday for not wearing a top hat, and Wednesday for not walking backward, you might complain about the arbitrariness of the rules, which are random, unpredictable, and without reason.
We often associate arbitrariness with dictators who make up laws and dish out punishments based on their moods or their desperate attempts to stay in power. At the same time, parents demonstrate a kind of arbitrariness when they answer the question "why not?" with "Because I said so!" To avoid arbitrariness, people make decisions based on consistency, reason, order, and predictability.