“Change is one thing. Acceptance is another.”

Three Roads to Quantum Gravity (2000)

Niebuhr's preferred form, as declared by his widow
The Serenity Prayer (c. 1942)
Variant: God, give us grace to accept with serenity the things that cannot be changed, courage to change the things which should be changed, and the wisdom to distinguish the one from the other.

Gaines response after being asked: "Do you also see things in that world that you wish could be retained?", as quoted by Marcia Gaudet and Carl WootonPorch in Talk with Ernest Gaines: Conversations on the Writer's Craft http://books.google.es/books?id=JtRNfST4g_QC&hl=es&source=gbs_navlinks_s (1990)

X, 11
Meditations (c. 121–180 AD), Book X
Context: Acquire the contemplative way of seeing how all things change into one another, and constantly attend to it, and exercise thyself about this part [of philosophy]. For nothing is so much adapted to produce magnanimity.... But as to what any man shall say or think about him, or do against him, he never even thinks of it, being himself contented with these two things: with acting justly in what he now does, and being satisfied with what is now assigned to him; and he lays aside all distracting and busy pursuits, and desires nothing else than to accomplish the straight course through the law, and by accomplishing the straight course to follow God.

Book B (sketchbook), c 1967: as quoted in Jasper Johns, Writings, sketchbook Notes, Interviews, ed. Kirk Varnedoe, Moma New York, 1996, p. 62
1960s

As quoted in "Mansfield Park and Film : An Interview with Patricia Rozema" by Hiba Moussa, in Literature/Film Quarterly 32, No. 4 (2004), p. 255
Context: You cannot underestimate what a radical thing it is to change from one art form to another. An author slaves to start with just the right word, phrase, sentence, and paragraph. The sounds of the words are crucial. But all the demands of words and prose are lifted when you make a movie. The physical presence makes many unnecessary and some necessary ones impossible. So you serve two masters as an adapting filmmaker: the author's intention and the needs of film. Sometimes "fidelity" can mean only focusing on one day of a story told over twenty years in a book.

Source: Assassin's Quest

One of the most commonly quoted forms.
The Serenity Prayer (c. 1942)
Variant: Lord, grant me the strength to accept the things I cannot change,
he courage to change the things I can,
and the wisdom to know the difference.

Source: The Best of Me