It dawned on me recently. Though nowadays most people live either on their own or with their spouse and/or a couple of minor children, and the houses are big and spacious, not so long ago even wealthier among us often had to share their house with relatives and servants, and the children were often quite numerous and stayed at home much longer than now.
In books like those about Miss Silver you can see that this Victorian habit of living all together survived even into late fifties and it was not uncommon for childless couples and singles to share a small family type hotel where each would have his separate room/s but would share meals and bathrooms.
In a situation like this it's of crucial importance that people don't become too familiar with each other and keep some privacy while on the other hand, they always stay polite and neighbourly, otherwise you can expect all sorts of nasty fights and general unpleasantness. It also helps when folks share some common concepts like the hour at which they eat their meals, for instance, otherwise you have a chaos when each household member eats at his own time and the kitchen is always a mess.
Another thing that helps is tolerance of others. It's strange that though our society supposedly increases in tolerance each day, people actually hardly tolerate each other any more. They prefer to socialise with their computer or TV set, they seldom talk to their neighbours, they drop their friends whenever it suits them and hardly even care about their own blood relatives, when they can't extract any profit out of them.
It has become fashionable to criticise egoistic baby-boomers who spend their time and money going on luxurious vacations now they are retiring yet nobody asks why they should keep the inheritance for their children and nephews/nieces when they hardly get any attention from them, either. There used to be a time when people hanged out with their second and third cousins, now they probably don't even know their names. So may be, we don't need manners, after all?