“Prismatic is the only word for those frightful tweeds and, oddly enough, the spectacle of them had the effect of steadying my nerves. They gave me the feeling that nothing mattered.”

Letter to Dionigi di Borgo San Sepolcro (26 April 1336), as translated by James Harvey Robinson (1898)
Context: My brother, waiting to hear something of St. Augustine's from my lips, stood attentively by. I call him, and God too, to witness that where I first fixed my eyes it was written: "And men go about to wonder at the heights of the mountains, and the mighty waves of the sea, and the wide sweep of rivers, and the circuit of the ocean, and the revolution of the stars, but themselves they consider not." I was abashed, and, asking my brother (who was anxious to hear more), not to annoy me, I closed the book, angry with myself that I should still be admiring earthly things who might long ago have learned from even the pagan philosophers that nothing is wonderful but the soul, which, when great itself, finds nothing great outside itself. Then, in truth, I was satisfied that I had seen enough of the mountain; I turned my inward eye upon myself, and from that time not a syllable fell from my lips until we reached the bottom again. Those words had given me occupation enough, for I could not believe that it was by a mere accident that I happened upon them. What I had there read I believed to be addressed to me and to no other, remembering that St. Augustine had once suspected the same thing in his own case, when, on opening the book of the Apostle, as he himself tells us, the first words that he saw there were, "Not in rioting and drunkenness, not in chambering and wantonness, not in strife and envying. But put ye on the Lord Jesus Christ, and make not provision for the flesh, to fulfil the lusts thereof."

Source: The Black Company (1984), Chapter 6, “Lady” (p. 205)

Aequanimitas (1889)
Context: In a true and perfect form, imperturbability is indissolubly associated with wide experience and an intimate knowledge of the varied aspects of disease. With such advantages he is so equipped that no eventuality can disturb the mental equilibrium of the physician; the possibilities are always manifest, and the course of action clear. From its very nature this precious quality is liable to be misinterpreted, and the general accusation of hardness, so often brought against the profession, has here its foundation. Now a certain measure of insensibility is not only an advantage, but a positive necessity in the exercise of a calm judgment, and in carrying out delicate operations. Keen sensibility is doubtless a virtue of high order, when it does not interfere with steadiness of hand or coolness of nerve; but for the practitioner in his working-day world, a callousness which thinks only of the good to be effected, and goes ahead regardless of smaller considerations, is the preferable quality.
Cultivate, then, gentlemen, such a judicious measure of obtuseness as will enable you to meet the exigencies of practice with firmness and courage, without, at the same time, hardening "the human heart by which we live."

Source: The Virgin Suicides

Sec. 115
Some Thoughts Concerning Education (1693)

Source: Shadows Linger (1984), Chapter 15, “Juniper: Death of a Gangster” (p. 287)

"In Time Of Plague," in The Man With Night Sweats (1992)
Other

Source: A Wind in the Door

Source: Message in a Bottle