"A good city street neighborhood achieves a marvel of balance between its people's determination to have essential privacy and their simultaneous wishes for differing degrees of contact, enjoyment or help from the people around. This balance is largely made up of small, sensitively managed details, practiced and accepted so casually that they are normally taken for granted...
"...consider the line drawn by Mr. Jaffe at the candy store around our corner -- a line so well understood by his customers and by other shopkeepers too that they can spend their whole lives in its presence and never think about it consciously. One ordinary morning last winter, Mr. Jaffe... supervised the small children crossing at the corner on the way to P.S. 41...; lent an umbrella to one customer and a dollar toanother; took custody of two keys; took in some packages for people in the next building who were away; lectured two youngsters who asked for cigarettes;... took custody of a watch to give the repair man across the street when he opened later; ...listened to a tale of domestic difficulty and offered reassurance; ...advised a mother who came for a birthday present not to get the ship-model kit because another child going to the same birthday party was giving that...
"After considering this multiplicity of extra-merchandising services I asked Bernie, 'Do you ever introduce your customers to each other?'
"He looked startled at the idea, even dismayed. 'No,' he said thoughtfully. 'That would just not be advisable. Sometimes, if I know two customers who are in the at the same time have an interest in common, I bring up the subject in conversation and let them carry it on from there if they want to. But oh no, I wouldn't introduce them.'
"...The line between the city public world and the world of privacy... can be maintained, without awkwardness to anyone, because of the great plenty of opportunities for public contact in the enterprises along the sidewalks, or on the sidewalks themselves as people move to and fro or deliberately loiter when they feel like it, and also because of the presence of many public hosts, so to speak, proprietors of meeting places like Bernie's where one is free either to hang around or dash in and out, no strings attached.
"Under this system, it is possible in a city street neighborhood to know all kinds of people without unwelcome entanglements, without boredom, necessity for excuses, explanations, fears of giving offense, embarrasssments respecting impositions or commitments, and all such paraphernalia of obligations which can accompany less limited relationships. It is possible to be on excellent sidewalk terms with people who are very different from oneself, and even, as time passes, on familiar public terms with them. Such relationships can, and do, endure for many years, for decades; they could never have formed without that line, much less endured. They form precisely because they are by-the-way to people's normal public sorties."

-- Jane Jacobs, The Death and Life of Great American Cities, 1992 edition, pp 58-61. (bold and typos are mine)