If a man does not make new acquaintance as he advances through life, he will soon find himself left alone. A man, Sir, should keep his friendship in constant repair.

Johnson, Samuel and James Boswell. "The Journal of a Tour to the Hebrides." A Journey to the Western Islands of Scotland and the Journal of a Tour to the Hebrides, edited by Jack Lynch and Celia Barnes. Oxford University Press, 2021.

Kant, Immanuel. Groundwork of the Metaphysics of Morals, translated by Mary Gregor and Jes Timmermann. Cambridge University Press, 2012.

Aristotle. Quoted in The Lives of Eminent Philosophers, written by Diogenes Laërtius, translated by Pamela Mensch, edited by James Miller. Oxford University Press, 2018, bk. 5, ch. 1, sect. 20.