“Only yesterday the practical things of today were decried as impractical, and the theories which will be practical tomorrow will always be branded as valueless games by the practical man of today.”

Source: Quoted in "Paul Sloane Quotes on Goodreads https://www.goodreads.com/quotes/770591-implementing-best-practice-is-copying-yesterday-innovation-is-inventing-tomorrow/ (1 April 2013)

Michel Henry, Marx I. une philosophie de la réalité, éd. Gallimard, coll. « Nrf », 1976, p. 353
Books on Economy and Politics, Marx. A Philosophy of Human Being (1976)
Original: (fr) Parce que la pratique est subjective, la théorie qui est toujours la théorie d’un objet, ne peut atteindre la réalité de cette pratique, ce qu’elle est en elle-même, sa subjectivité précisément, mais seulement se la représenter, de telle manière que cette représentation laisse hors d’elle l’être réel de la pratique, l’effectivité du faire. La théorie ne fait rien.

"Tomorrow" (1919), as translated in A Soviet Heretic : Essays by Yevgeny Zamyatin (1970) edited and translated by Mirra Ginsburg
Context: Yesterday, there was a tsar, and there were slaves; today there is no tsar, but the slaves remain; tomorrow there will be only tsars. We march in the name of tomorrow's free man — the royal man. We have lived through the epoch of suppression of the masses; we are living in an epoch of suppression of the individual in the name of the masses; tomorrow will bring the liberation of the individual — in the name of man. Wars, imperialist and civil, have turned man into material for warfare, into a number, a cipher. Man is forgotten, for the sake of the sabbath. We want to recall something else to mind: that the sabbath is for man.
The only weapon worthy of man — of tomorrows's man — is the word.

Source: War and Peace

Source: The Lost Thing

Source: The New Left: The Anti-Industrial Revolution (1971), p. 167

1950s, Loving Your Enemies (Christmas 1957)

The Black Coat (2013)

Attributed in Nassim Nicholas Taleb, Antifragile - Things that Gain From Disorder (2012), p. 213.
The earliest known appearance of this quote in print is Walter J. Savitch, Pascal: An Introduction to the Art and Science of Programming (1984), where it is attributed as a "remark overheard at a computer science conference". It circulated as an anonymous saying for more than ten years before attributions to Jan L. A. van de Snepscheut and Yogi Berra began to appear (and later still to various others).
Disputed, Misattributed