“Virtue (or the man of virtue) is not left to stand alone. He who practices it will have neighbors.”
Source: The Analects, Chapter IV
Original
德不孤,必有鄰。
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Confucius 269
Chinese teacher, editor, politician, and philosopher -551–-479 BCRelated quotes

Vice and Virtue, ii
The Note-Books of Samuel Butler (1912), Part II - Elementary Morality

Source: The Doctrine of the Mean

“It is the enemy who can truly teach us to practice the virtues of compassion and tolerance.”
Ocean of Wisdom: Guidelines for Living (1989) ISBN 094066609X
Unsourced variant: In the practice of tolerance, one's enemy is the best teacher.

Source: The Tales of Alvin Maker, Alvin Journeyman (1995), Chapter 2.

“A minimum of comfort is necessary for the practice of virtue.”
Congo, My Country

“He left a corsair's name to other times,
Linked with one virtue, and a thousand crimes.”
Canto III, stanza 24; this can be compared to: "Hannibal, as he had mighty virtues, so had he many vices; he had two distinct persons in him", Robert Burton, Anatomy of Melancholy, "Democritus to the Reader".
The Corsair (1814)

Celui qui étudie un texte ou des microbes ou les étoiles doit se défaire de sa subjectivité... c'est là un idéal qu'il faut essayer de rejoindre par une certaine pratique. Disons que l'objectivité est une vertu, d'ailleurs très diffice à pratiquer.
La Philosophie comme manière de vivre (2001)