“ A man, we say, should look like his trade and profession; yet the pedantry of every profession is disagreeable. The different periods of life have, for the same reason, different manners assigned to them. ”
 Adam Smith, The Theory of Moral Sentiments (1759). copy citation

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“But as in each species of things, we are particularly pleased with the middle conformation, which, in every part and feature, agrees most exactly with the general standard which nature seems to have established for things of that kind; so in each rank, or, if I may say so, in each species of men, we are particularly pleased, if they have neither too much, nor too little of the character which usually accompanies their particular condition and situation. A man, we say, should look like his trade and profession; yet the pedantry of every profession is disagreeable. The different periods of life have, for the same reason, different manners assigned to them. We expect in old age, that gravity and sedateness which its infirmities, its long experience, and its worn-out sensibility seem to render both natural and respectable; and we lay our account to find in youth that sensibility, that gaiety and sprightly vivacity which experience teaches us to expect from the lively impressions that all interesting objects are apt to make upon the tender and unpractised senses of that early period of life.” source