To avoid chaos in the bad, non-technical sense of the word, anarchy requires rules, because independent individual actions must be coordinated in some way. Rule-based anarchy is, as James Buchanan puts it, "ordered anarchy." Whether ordered anarchy can extend to all areas of social life, whether or not we need the state at all, is a question that need not concern us here. We may simply accept, for now, that a social system based on property rights and freedom of contract is "real anarchism, feasible and realized, and not mere emotional rhetoric," as French philosopher Raymond Ruyer argued in his In Praise of the Consumer Society.
We follow rules because they are necessary to coordinate individual actions in a social setting. Some rules are self-enforcing, i.e., it is in each individual's interest to obey them. For example, once more than 50% of car operators drive on the right side of the road in a particular area, more and more drivers will notice that adapting to this rule reduces their risks of accident, and the rule will become more and more accepted. A driver who decides to break the rule will risk incurring a high cost.
A related reason why we follow rules is that we don't know the consequences of particular decisions: rules are, as Hayek says, "a device for coping with our constitutional ignorance." Consider the following example. You meet Hitler when he is five years old. Should you shoot him (assuming the tyrant has let you have a gun)? Yes, of course, but only if you are 100% sure that he will indeed become the Führer of the Third Reich. Since you cannot have such a certainty and the child you are meeting may instead turn out to be another Friedrich Hayek, you should not shoot. The rule against killing future potential killers is a useful rule, because we cannot know all the particular circumstances of a given situation.
Because of our ignorance of all particular circumstances, self-imposed rules are often in one's own interest. I, for example, could decide to work at night and sleep during the day. One inconvenient is that I don't know who may try to reach me during business hours tomorrow, while I am pretty sure that nobody will try during the night. So, my interest is to be awake when most people expect me to be. Another example, closer to etiquette: I could, every morning, decide whether to shave or not depending on my plans for the day, but a rule of the kind "always shave in the morning" is useful (for many people) because one never knows if some unforeseen circumstances (an impromptu visit, for example) will not require one to be clean shaven.
Another reason for following rules is that evolved rules are likely to incorporate useful implicit knowledge – i.e., knowledge that we don't possess in the sense that we can't explain it, but which represents an efficient adaptation to our ignorance. A simple example is given by the rules of thumb that had developed, for example, in shipbuilding, when engineering was not advanced enough to provide scientific formulas for, say, the optimal sizes and shapes of hulls. Sociological illustrations are given by complex social rules such as language, property rights, free markets, relations between the sexes, or family management.
In certain instances, we follow rules because we want to guard against particular decisions that may, on the spur of the moment, bring satisfaction, but have long term consequences we wish to avoid. You may use a loud, or repeating, alarm-clock, or put it out of reach, because you know that you may be tempted to stay in bed when the time comes. Similarly –this is James Buchanan's constitutional economic perspective – individuals may want to limit the state so as to prevent some political decisions that may eventually appear desirable to a majority.
Some people follow rules for moral reasons. But such moral rules may have evolved for the sort of reasons we described, i.e., because they are efficient at coordinating individual actions in the face of uncertainty and ignorance, and because they were selected precisely for this purpose.
Of course, not all rules are useful and worth following. Explicit knowledge may make rules obsolete (like in the shipbuilding example). More efficient rules may be discovered. Rules (and for social institutions, which are complexes of rules) therefore need to be open to criticism. The challenge of efficiency is, in large part, to follow efficient rules and to discard inefficient ones. The social institutions that have developed in the West are relatively efficient precisely because individual liberty allows for diversified experiments which challenge rules and lead to their replacement when needed.
The usefulness of rules and the simultaneous importance of individual liberty for challenging them are well illustrated by the world of finance. The complex financial institutions that have developed over the past two centuries – from those governing shares of stock and stock exchanges to those generating financial derivatives – are based on rules accepted by market participants. Indeed, following rules is considered so important by them that they tend to focus on knowing the rules, whatever they are, provided that they are reliable. They tend to forget that reliability is not the only desirable characteristic of rules: rules also have to adapt to changed circumstances and market demands. Now, such flexibility is only possible in a context of individual liberty, i.e., in free financial markets, where rules are voluntarily agreed, and generated, by contracting parties. When financial executives are willing to accept any kind of rules from the state (like those enforced by the Securities and Exchange Commission) provided that they are clear, they are cutting the branch on which their efficiency rests.
Rules are indispensable, but there must be ways to challenge them by trying new ones. Much of the art of social, and personal, life is about knowing which rules to follow and which rules to disobey. As surrealist, and classical liberal, author André Thirion wrote, we must "know how to disobey" ("savoir désobéir").