Why "small"?
Costs it more pain that this ye call
A "great event" should come to pass
From that? Untwine me from the mass
Of deeds which make up life, one deed
Power shall fall short in or exceed!
Introduction.
Pippa Passes (1841)

“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.”

Robert Browning Men and Women

"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)

“That low man seeks a little thing to do,
Sees it and does it.
This high man, with a great thing to pursue,
Dies ere he knows it.
That low man goes on adding one to one,—
His hundred's soon hit;
This high man, aiming at a million,
Misses an unit.
That has the world here—should he need the next,
Let the world mind him!
This throws himself on God, and unperplexed
Seeking shall find him.”

Robert Browning Men and Women

"A Grammarian's Funeral", line 115.
Men and Women (1855)

“Forgive me this digression — that I stand
Entranced awhile at Law's first beam, outbreak
O' the business, when the Count's good angel bade
"Put up thy sword, born enemy to the ear,
"And let Law listen to thy difference!"”

Robert Browning The Ring and the Book

And Law does listen and compose the strife,
Settle the suit, how wisely and how well!
On our Pompilia, faultless to a fault,
Law bends a brow maternally severe,
Implies the worth of perfect chastity,
By fancying the flaw she cannot find.
Book IX : Juris Doctor Johannes-Baptista Bottinius, Fisci et Rev. Cam. Apostol. Advocatus.
The Ring and the Book (1868-69)

“Error has no end.”

Robert Browning Paracelsus

Part 3.
Paracelsus (1835)

“Deeds let escape are never to be done.”

Robert Browning book Sordello

Book the Third
Sordello (1840)

“Strive and thrive!”

Robert Browning

Asolando, "Epilogue" (1889).

“It's wiser being good than bad;
It's safer being meek than fierce;
It's fitter being sane than mad.
My own hope is, a sun will pierce
The thickest cloud earth ever stretched;
That after Last returns the First,
Though a wide compass round be fetched;
That what began best can't end worst,
Nor what God blessed once prove accurst.”

Robert Browning

Apparent Failure, vii.
Bartlett's Familiar Quotations, 10th ed. (1919)