That's what a reasonable person, a person with good manners, would do.
Interview with Marion Finlay, "Hockney on … politics, pleasure, and smoking in public places," FOREST Online (28 July 2004)
2000s
“In cities people think that it is good manners not even to know who lives in the same building.”
In Städten glaubt man, es gehöre zum guten Tone, nicht einmal zu wissen, wer in demselben Hause wohnt.
Quoted in Der kleine Rechthaber: Wem gehört die Parklücke und andere juristische Überraschungen (2008) by Claus Murken, p. 79.
Original
In großen Städten gehört es leider zum guten Tone, nicht einmal zu wissen, wer mit uns in demselben Hause wohne.
Zweites Buch, 8. Kapitel, Haus, Hausgenossen, Nachbarn, Wirt und Gast. hg. von Karl Goedeke. 16. Ausgabe. Hannover: Hahn, 1878. Seite 203 http://commons.wikimedia.org/w/index.php?title=Image%3A%C3%9Cber_den_Umgang_mit_Menschen.djvu&page=219
Über den Umgang mit Menschen
Variant: In Städten glaubt man, es gehöre zum guten Tone, nicht einmal zu wissen, wer in demselben Hause wohnt.
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Adolph Freiherr Knigge 20
German writer and Freemason 1752–1796Related quotes
Source: In Kirovohrad foundation stone of church was blessed http://news.ugcc.ua/en/news/in_kirovohrad_foundation_stone_of_church_was_blessed_57087.html (30 November 2009)

“I want to live in a city where the people who make the rules have to live by them.”
"I Want to Live in a City Where..." (2006)
Variant: I want to live in a city where half the people in charge are women.
On how being a city planner affects her writing in “Questions For Arkady Martine, Author Of 'A Memory Called Empire'” https://www.npr.org/2019/04/07/710356506/questions-for-arkady-martine-author-of-a-memory-called-empire in NPR (2019 Apr 7)

My bright idea: Civilisation is still worth striving for

Source: My Double Life (1907), Ch. 33 <!-- p. 369 -->
Context: Life is short, even for those who live a long time, and we must live for the few who know and appreciate us, who judge and absolve us, and for whom we have the same affection and indulgence. The rest I look upon as a mere crowd, lively or sad, loyal or corrupt, from whom there is nothing to be expected but fleeting emotions, either pleasant or unpleasant, which leave no trace behind them. We ought to hate very rarely, as it is too fatiguing; remain indifferent to a great deal, forgive often and never forget.

As quoted in Friends' Intelligencer Vol. XI (1854), p. 821