From John Stuart Mill's On Liberty, Chapter 3 “Of Individuality, as One of the Elements of Well-Being,” paragraph 3:
Nobody denies that people should be so taught and trained in youth, as to know and benefit by the ascertained results of human experience. But it is the privilege and proper condition of a human being, arrived at the maturity of his faculties, to use and interpret experience in his own way. It is for him to find out what part of recorded experience is properly applicable to his own circumstances and character. The traditions and customs of other people are, to a certain extent, evidence of what their experience has taught them;presumptive evidence, and as such, have a claim to his deference: but, in the first place, their experience may be too narrow; or they may not have interpreted it rightly. Secondly, their interpretation of experience may be correct, but unsuitable to him. Customs are made for customary circumstances, and customary characters; and his circumstances or his character may be uncustomary. Thirdly, though the customs be both good as customs, and suitable to him, yet to conform to custom, merely as custom, does not educate or develop in him any of the qualities which are the distinctive endowment of a human being. The human faculties of perception, judgment, discriminative feeling, mental activity, and even moral preference, are exercised only in making a choice. He who does anything because it is the custom, makes no choice. He gains no practice either in discerning or in desiring what is best. The mental and moral, like the muscular powers, are improved only by being used.