WIST

The end of Man is an Action and not a Thought, though it were the noblest.

Thomas Carlyle (1795-1881) Scottish essayist and historian
Sartor Resartus, Book 2, ch. 6 (1836)

Easy reading is damn hard writing.

Nathaniel Hawthorne (1804-1864) American writer
(Attributed)
Also attributed to others, including Ernest Hemingway. Per Wikiquote, the earliest use of the phrase found as such is by Maya Angelou, in Conversations With Maya Angelou (1989) [ed. Jeffrey M. Elliot]

I think it's Alexander Pope who says, "Easy writing is damn hard reading," and vice versa, easy reading is damn hard writing.

Which may refer in turn not to Pope but Richard Brinsley, Clio's Protest, or the Picture Varnished (1771, pub. 1819):

You write with ease, to show your breeding, But easy writing's curst hard reading.

And what is this smile of the world, to win which we are bidden to sacrifice our moral manhood; this frown of the world, whose terrors are more awful than the withering up of truth and the slow going out of light within the souls of us?

John, Viscount Morley (1838-1923) English politician and writer
On Compromise, ch. 4 (1877)

That a marriage ends is less than ideal; but all things end under heaven, and if temporality is held to be invalidating, then nothing real succeeds.

John Updike (1932-2009) American writer
Too Far To Go, foreword (1979)

Practical equality of opportunity for all citizens, when we achieve it, will have two great results. First, every man will have a fair chance to make of himself all that in him lies; to reach the highest point to which his capacities, unassisted by special privilege of his own and unhampered by the special privilege of others, can carry him, and to get for himself and his family substantially what he has earned. Second, equality of opportunity means that the commonwealth will get from every citizen the highest service of which he is capable. No man who carries the burden of the special privileges of another can give to the commonwealth that service to which it is fairly entitled.

Theodore Roosevelt (1858-1919) US President (1901-1909)
“The New Nationalism,” speech, Osawatomie, Kansas (31 Aug 1910)