The spouses share the indifferent "intimacies" of the day, the amiable and the unpleasant features of every hour, and the weaknesses that remain carefully hidden from all others. This easily causes them to place the accent and the substance of their relationship upon these wholly individual but objectively irrelevant matters. It leads them to consider what they share with others and what perhaps is the most important part of their personalities objective, intellectual, generally interesting, generous features as lying outside the marital relation; and thus they gradually eliminate it from their marriage.

Georg Simmel, The Sociology of Georg Simm…, loc. 3806