"When an area of a city lacks a sidewalk life, the people of the place must enlarge their private lives if they are to have anything approaching equivalent contact with their neighbors. They must settle for some form of 'togetherness,' in which more is shared with one another than in the life o the sidewalks, or else they must settle for lack of contact. Inevitably the outcome is one or the other; it has to be; and either has distressing results.
   "In the case of the first outcome, where people do share much, they become exceedingly choosy as to who their neighbors are, or with whom they associate at all. They have to become so. A friend of mine, Penny Kostritsky, is unwittingly and unwillingly in this fix on a street in Baltimore. Her street of nothing but residences, embedded in an area of almost nothing but residences, has been experimentally equipped with a charming sidewalk park...
   "However, there are no stores. The mothers from nearby blocks who bring small children here, and come here to find some contact with others themselves, perforce go into the houses of acquaintances along the street to warm up in winter, to make telephone calls, to take their children in emergencies to the bathroom. Their hostesses offer them coffee, for there is no other place to get coffee, and naturally considerable social life of this kind has arisen around the park. Much is shared.
   "Mrs. Kostritsky, who lives in one of the conveniently located houses, and who has two small children, is in the thick of this narrow and accidental social life... Still more distressing, when mothers of different income or color or educational background bring their children to the street park, they and their children are rudely and pointedly ostracized. They fit awkwardly into the suburbanlike sharing of private lives that has grown in default of city sidewalk life.
   "...City residential planning that depends, for contact among neighbors, on personal sharing of this sort, and that cultivates it, often does work well socially, if rather narrowly, for self-selected upper-middle-class people. It solves easy problems for an easy kind of population. So far as I have been able to discover, it fails to work, however, even on its own terms, with any other kind of population.
   "The more common outcome in cities, where people are faced with the choice of sharing much or nothing, is nothing. In city areas that lack a natural and casual public life, it is common for residents to isolate themselves from each other to a fantastic degree. If mere contact with your neighbors threatens to entangle you in their private lives, or entangle them in yours, and if you cannot be so careful who your neighbors are..., the logical solution is absolutely to avoid friendliness or casual offers of help. Better to stay thoroughly distant. As a practical result, the ordinary public jobs -- like keeping children in hand -- for which people must take a little personal initiative, or those for which they must band together in limited common purposes, go undone. The abysses this opens up can be almost unbelievable."

-- Jane Jacobs, The Death and Life of Great American Cities, 1992 edition, pp 62-65. (bold and typos are mine)