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. The faculties are called into no exercise by doing a thing merely because others do it, no more than by believing a thing only because others believe it.

What It Means

This is a placeholder explanation generated by the low-overhead model. It interprets "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. The faculties are called into no exercise by doing a thing merely because others do it, no more than by believing a thing only because others believe it." in the context of "John Stuart Mill, On Liberty, 2nd ed. (Boston, MA: Ticknor & Fields, 1863), ch. 3, p. 112 https://archive.org/details/onliberty04millgoog/page/n118/mode/2up" to mean that wisdom is timeless.