The true explanation of the rule is the same as that which accounts for the law's indifference to a man's particular temperament, faculties, and so forth. Public policy sacrifices the individual to the general good. It is desirable that the burden of all should be equal, but it is still more desirable to put an end to robbery and murder. It is no doubt true that there are many cases in which the criminal could not have known that he was breaking the law, but to admit the excuse at all would be to encourage ignorance where the law-maker has determined to make men know and obey, and justice to the individual is rightly outweighed by the larger interests on the other side of the scales. [49] If the foregoing arguments are sound, it is already manifest that liability to punishment cannot be finally and absolutely determined by considering the actual personal unworthiness of the criminal alone. That consideration will govern only so far as the public welfare permits or demands. And if we take into account the general result which the criminal law is intended to bring about, we shall see that the actual state of mind accompanying a criminal act plays a different part from what is commonly supposed. For the most part, the purpose of the criminal law is only to induce external conformity to rule. All law is directed to conditions of things manifest to the senses. And whether it brings those conditions to pass immediately by the use of force, as when it protects a house from a mob by soldiers, or appropriates private property to public use, or hangs a man in pursuance of a judicial sentence, or whether it brings them about mediately through men's fears, its object is equally an external result. In directing itself against robbery or murder, for instance, its purpose is to put a stop to the actual physical taking and keeping of other men's goods, or the actual poisoning, shooting, stabbing, and otherwise putting to death of other men. If those things are not done, the law forbidding them is equally satisfied, whatever the motive.