“There is nothing less powerful than knowledge unattached, and incapable of application. That is why what little knowledge I have has done myself personally so much harm. I do not know much, but if I knew a good deal less than that little I should be far more powerful.”

"Andrea del Sarto", line 70
"Less is more" is often misattributed to architects Buckminster Fuller or Ludwig Mies van der Rohe. It is something of a motto for minimalist philosophy. It was used in 1774 by Christoph Martin Wieland.
Men and Women (1855)
Context: I do what many dream of, all their lives,
— Dream? strive to do, and agonize to do,
And fail in doing. I could count twenty such
On twice your fingers, and not leave this town,
Who strive — you don't know how the others strive
To paint a little thing like that you smeared
Carelessly passing with your robes afloat —
Yet do much less, so much less, Someone says,
(I know his name, no matter) — so much less!
Well, less is more, Lucrezia: I am judged.
There burns a truer light of God in them,
In their vexed beating stuffed and stopped-up brain,
Heart, or whate'er else, than goes on to prompt
This low-pulsed forthright craftsman's hand of mine.

Source: Way Station (1963), Ch. 11
Context: There was so much knowledge in the galaxy and he knew so little of it, understood so little of the little that he knew.
There were men on Earth who could make sense of it. Men who would give anything short of their very lives to know the little that he knew, and could put it all to use.
Out among the stars lay a massive body of knowledge, some of it an extension of what mankind knew, some of it concerning matters which Man had not yet suspected, and used in ways and for purposes that Man had not as yet imagined. And never might imagine, if left on his own.

Book III, Ch. 9
Essais (1595), Book III

Source: The Two Cultures and the Scientific Revolution (1959), P. 10

"Suni Lee talks gold medal win, 'cherished' backyard balance beam she trained on as a kid" in Today (30 July 2021) https://www.today.com/news/suni-lee-talks-gold-medal-win-i-still-can-t-t226952

Letter to Frederick Ayers (5 May 1943), published in The Patton Papers 1940-1945 (1996) edited by Martin Blumenson, p. 242
Context: The publicity I have been getting, a good deal of which is untrue, and the rest of it ill considered, has done me more harm than good. The only way you get on in this profession is to have the reputation of doing what you are told as thoroughly as possible. So far I have been able to accomplish that, and I believe I have gotten quite a reputation from not kicking at peculiar assignments.

Isaac D'Israeli, Curiosities of Literature.
Misattributed, Isaac D'Israeli

Source: Three Lives & Tender Buttons