The Theory of Moral Sentiments by Adam Smith

There are other principles besides those already enumerated, which have a considerable influence upon the moral sentiments of mankind, and are the chief causes of the many irregular and discordant opinions which prevail in different ages and nations concerning what is blamable or praiseworthy. These principles are custom and fashion, principles which extend their dominion over our judgments concerning beauty of every kind.

When two objects have frequently been seen together, the imagination acquires a habit of passing easily from the one to the other. If the first appear, we lay our account that the second is to follow. Of their own accord they put us in mind of one another, and the attention glides easily along them. Though, independent of custom, there should be no real beauty in their union, yet when custom has thus connected them together, we feel an impropriety in their separation. The one we think is awkward when it appears without its usual companion. We miss something which we expected to find, and the habitual arrangement of our ideas is disturbed by the disappointment. A suit of clothes, for example, seems to want something if they are without the most insignificant ornament which usually accompanies them, and we find a meanness or awkwardness in the absence even of a haunch button. When there is any natural propriety in the union, custom increases our sense of it, and makes a different arrangement appear still more disagreeable than it would otherwise seem to be. Those who have been accustomed to see things in a good taste, are more disgusted by whatever is clumsy or awkward. Where the conjunction is improper, custom either diminishes, or takes away altogether, our sense of the impropriety. Those who have been accustomed to slovenly disorder lose all sense of neatness or elegance. The modes of furniture or dress which seem ridiculous to strangers, give no offence to the people who have been used to them.