“Writing laws is easy, but governing is difficult.”

Source: The Writings and Speeches of Daniel Webster: Diplomatic Papers and Miscellaneous Letters

Un Art de Vivre (The Art of Living) (1939), The Art of Thinking

I, line 30.
Satires, Satire I

Also attributed to Ernest Hemingway and others; the earliest definite occurrence of this yet found in research for Wikiquote is by Maya Angelou, who stated it in Conversations With Maya Angelou (1989) edited by 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
The statement she referred to is most probably:
You write with ease, to show your breeding,
But easy writing's curst hard reading
Clio's Protest, or the Picture Varnished (written 1771, published 1819) by Richard Brinsley Sheridan
Disputed

Miles Sparks, Prologue, p. 3
2000s, Three Weeks with My Brother (2004)

As quoted in Paris Was Our Mistress (1947) by Samuel Putnam, p. 128

“Is It Possible to Write a Poem?,” p. 111
The Sun Watches the Sun (1999), Sequence: “Is It Possible to Write a Poem”

Kerr v. Willan (1817), 2 Starkie, 54.

Clio's Protest (1819).