Lecture IX : On the Conduct of the Understanding.; this provides the origin of the phrase "a square peg in a round hole".
Elementary Sketches of Moral Philosophy (1849)
Context: It is a very wise rule in the conduct of the understanding, to acquire early a correct notion of your own peculiar constitution of mind, and to become well acquainted, as a physician would say, with your idiosyncrasy. Are you an acute man, and see sharply for small distances? or are you a comprehensive man, and able to take in, wide and extensive views into your mind? Does your mind turn its ideas into wit? or are you apt to take a common-sense view of the objects presented to you? Have you an exuberant imagination, or a correct judgment? Are you quick, or slow? accurate, or hasty? a great reader, or a great thinker? It is a prodigious point gained if any man can find out where his powers lie, and what are his deficiencies, — if he can contrive to ascertain what Nature intended him for: and such are the changes and chances of the world, and so difficult is it to ascertain our own understandings, or those of others, that most things are done by persons who could have done something else better. If you choose to represent the various parts in life by holes upon a table, of different shapes, — some circular, some triangular, some square, some oblong, — and the persons acting these parts by bits of wood of similar shapes, we shall generally find that the triangular person has got into the square hole, the oblong into the triangular, and a square person has squeezed himself into the round hole. The officer and the office, the doer and the thing done, seldom fit so exactly, that we can say they were almost made for each other.
Sydney Smith: Man
Sydney Smith was English writer and clergyman. Explore interesting quotes on man.
Referring to the lack of established culture and the established institution of slavery in the United States, in "Review of Seybert’s Annals of the United States", published in The Edinburgh Review (1820)
Context: In the four quarters of the globe, who reads an American book? Or goes to an American play? or looks at an American picture or statue? What does the world yet owe to American physicians or surgeons? What new substances have their chemists discovered? Or what old ones have they advanced? What new constellations have been discovered by the telescopes of Americans? Who drinks out of American glasses? Or eats from American plates? Or wears American coats or gowns? or sleeps in American blankets? Finally, under which of the old tyrannical governments of Europe is every sixth man a slave, whom his fellow-creatures may buy and sell and torture?
Vol. I, p. 130
Lady Holland's Memoir (1855), Bartlett's Familiar Quotations, 10th ed. (1919)

“He was a one-book man. Some men have only one book in them; others, a library.”
Vol. I, ch. 11
Lady Holland's Memoir (1855)
“It is always right that a man should be able to render a reason for the faith that is within him.”
Vol. I, p. 53
Lady Holland's Memoir (1855), Bartlett's Familiar Quotations, 10th ed. (1919)
Peter Plymley's Letters (1808), Letter IV
Lecture IX : On the Conduct of the Understanding
Elementary Sketches of Moral Philosophy (1849)