The liberty of the individual must be thus far limited; he must not make himself a nuisance to other people. But if he refrains from molesting others in what concerns them, and merely acts according to his own inclination and judgement in things which concern himself, the same reasons which show that opinions should be free prove also that he should be allowed, without molestation, to carry his opinions into practice at his own cost. That mankind are not infallible; that their truths for the most part are only half-truths; that unity of opinion, unless resulting from the fullest and freest comparison of opposite opinions, is not desirable, and diversity not an evil but a good, until mankind are much more capable than at present of recognizing all sides of the truth, are principles applicable to men's modes of action not less than to their opinions. As it is useful that while mankind are imperfect there should be different opinions, so it is that there should be different experiments of living; that free scope should be given to varieties of characters, short of injury to others; and that the worth of different modes of life should be proved practically, when anyone thinks fit to try them. It is desirable, in short, that in things which do not primarily concern others, individuality should assert itself. Where, not the person's own character but the traditions or customs of other people are the rule of conduct, there is wanting one of the principal ingredients of human happiness and quite the chief ingredient of individual and social progress.