“There’s nothing quite so pernicious as wishful thinking.”

The Autocrat of the Breakfast Table (1858)
Context: Nothing is so common-place as to wish to be remarkable. Fame usually comes to those who are thinking about something else, - very rarely to those who say to themselves, "Go to, now, let us be a celebrated individual!"

Colonel John Boyle and David in Ch. 7
Source: The Garden of Eden (1986)

As quoted in "The Gentle Philosopher" (2006) by John Little at the Will Durant Foundation https://web.archive.org/web/20130312115951/http://www.willdurant.com/home.html
Context: It is a mistake to think that the past is dead. Nothing that has ever happened is quite without influence at this moment. The present is merely the past rolled up and concentrated in this second of time. You, too, are your past; often your face is your autobiography; you are what you are because of what you have been; because of your heredity stretching back into forgotten generations; because of every element of environment that has affected you, every man or woman that has met you, every book that you have read, every experience that you have had; all these are accumulated in your memory, your body, your character, your soul. So with a city, a country, and a race; it is its past, and cannot be understood without it.

Source: The Wealth of Nations (1776), Book I, Chapter IX, p. 117.
Context: Our merchants and master-manufacturers complain much of the bad effects of high wages in raising the price, and thereby lessening the sale of their goods both at home and abroad. They say nothing concerning the bad effects of high profits. They are silent with regard to the pernicious effects of their own gains. They complain only of those of other people.

Variant: There is nothing so useless as doing efficiently that which should not be done at all.

If This Goes On— (p. 401)
Short fiction, The Past Through Tomorrow (1967)

Source: Dictionary of Burning Words of Brilliant Writers (1895), P. 112.

Greek Exercises (1888); at the age of fifteen, Russell used to write down his reflections in this book, for fear that his people should find out what he was thinking.
Youth