The mind must rest as well as work. To write too much ruins it; to leave off writing rusts it.
[tr. Attwell (1896), ¶ 336]

One ruins the mind with too much writing. One rusts it by not writing at all.
[tr. Auster (1983), 1805 entry]

Several things are insupportable if they are but indifferent, as Poetry, Music, Painting and Public Speeches.
'Tis the worst punishment in the world to hear a dull Declamation deliver'd with Pomp and Solemnity, and bad Verses rehears'd with the Emphasis of a wretched Poet.
[Bullord ed. (1696)]

Somethings are insupportable if they are but indifferent, as Poetry, Musick, Painting, and Publick Speeches.
What a Punishment is it to hear a cold Declamation deliver'd with Pomp and Solemnity, and indifferent Verses repeated with all the Emphasis of a bad Poet!
[Curll ed. (1713)]

Some things won't bear a Mediocrity, as Poetry, Musick, Painting and Oratory.
What a cruel Torture is it to hear a dull Declamation delivered with Pomp and Solemnity, or bad Verses rehearsed with the Emphasis of a wretched Poet!
[Browne ed. (1752)]

In certain things mediocrity is unbearable, as in poetry, music, painting, and eloquence. How we are tortured when we hear a dull soliloquy delivered in a pompous tone, or indifferent verses read with all the emphasis of a wretched poet!
[tr. Van Laun (1885)]

There are some things that will not bear mediocrity; poetry, music, painting, oratory.
[tr. Lee (1903)]

If breath and vigour, by indulgent Heav'n,
To sing this bev'rage of the Gods were giv'n,
What holy rapture would exalt my Song!
To tell the unexhausted sweets that flow
From that blest Fountain o'er the Vale below.
And warm, with new desire, the votive Throng!
But now the Muse has run her fatal round,
And mark'd her Circle to the Second Bound.
[tr. Boyd (1802), st. 26-27]

Were further space allow’d,
Then, Reader, might I sing, though but in part,
That beverage, with whose sweetness I had ne’er
Been sated. But, since all the leaves are full,
Appointed for this second strain, mine art
With warning bridle checks me.
[tr. Cary (1814)]

Reader, had I but longer space to write,
I might describe to thee, in part, the taste
Of draught that's ever sweet, nor waste
The time; but leaves are all already full
Appointed for the second canticle,
Nor curb nor rein permit me use the will.
[tr. Bannerman (1850)]

If, Reader, I possessed a longer space
For writing it, I yet would sing in part
Of the sweet draught that ne'er would satiate me;
But inasmuch as full are all the leaves
Made ready for this second canticle,
The curb of art no farther lets me go.
[tr. Longfellow (1867)]

If I had, reader, longer space to write, I should sing, at all events in part, the sweet draught which never would have sated me; but, for that all the sheets put in frame for this second Canticle are full, the bridle of my art lets me go no further.
[tr. Butler (1885)]

Reader, if longer space to me were rated
For writing, I would strive to sing in part
That draught so sweet, which never could have sated.
But since is now completely filled the chart
Allotted for this second book, there leaves
No power to wander more the curb of Art.
[tr. Minchin (1885)]

If I had, Reader, longer space for writing I would yet partly sing the sweet draught which never would have sated me. But, because all the leaves destined for this second canticle are full, the curb of my art lets me go no further.
[tr. Norton (1892)]

If, reader, I had greater space for writing, I would sing, at least in part, of the sweet draught which never would have sated me;
but forasmuch as all the pages ordained for this second canticle are filled, the curb of art no further lets me go.
[tr. Okey (1901)]

If, reader, I had more space to write I should sing but in part the sweet draught which never would have sated me; but since all the sheets prepared for this second cantica are full the curb of art does not let me go farther.
[tr. Sinclair (1939)]

If, Reader, for the writing were more space,
That sweet fount, whence I ne'er could drink my fill,
Would I yet sing, though in imperfect praise.
But seeing that for this second canticle
The paper planned is full to the last page,
The bridle of art must needs constrain my will.
[tr. Binyon (1943)]

If for my writing, Reader, I'd more space,
I'd sing -- at least in part -- those sweets my heart
Might aye have drunk nor e'er known weariness;
But since I've filled the pages set apart
For this my second cantique, I'll pursue
No further, bridled by the curb of art.
[tr. Sayers (1955)]

If, reader, I had greater space for writing
I would yet partly sing the sweet draught
which never would have sated me.
but since all the pages ordained
for this second canticle are filled,
the curb of art lets me go no further.
[tr. Singleton (1973)]

Reader, if I had space to write more words,
I'd sing, at least in part, of that sweet draught
which never could have satisfied my thirst;
But now I have completed every page
planned for my poem's second canticle --
I am checked by the bridle of my art!
[tr. Musa (1981)]

If, reader, I had room to write more,
My poem could still not tell you everything
About the sweet drink of which I could never have had enough.
But since all the pages designed for this
Second part of the poem have been filled,
The rules of art stop me at this point.
[tr. Sisson (1981)]

If, reader, I had ampler space in which
to write, I'd sing -- though incompletely -- that
sweet draught for which my thirst was limitless;
but since all of the pages pre-disposed
for this, the second canticle, are full,
the curb of art will not let me continue.
[tr. Mandelbaum (1982)]

Reader, if I had more space to write, I would speak, partially at least, about that sweet drink, which would never have sated me: but because all the pages determined for the second Canticle are full, the curb of art lets me go no further.
[tr. Kline (2002)]

If, reader, I had more space to write, I would continue to sing in part the sweet drink that could never satiate me,
but because all the pages are filled that have been laid out for this second canticle, the bridle of art permits me to go no further.
[tr. Durling (2003)]

If, reader, I'd more space in which to write,
then I should sing in part about that drink,
so sweet I’d never have my fill of it.
However, since these pages now are full,
prepared by rights to take the second song,
the reins of art won't let me pass beyond.
[tr. Kirkpatrick (2007)]

If, reader, I had more ample space to write,
I should sing at least in part the sweetness
of the drink that never would have sated me,
but, since all the sheets
readied for this second canticle are full,
the curb of art lets me proceed no farther.
[tr. Hollander/Hollander (2007)]

O reader, if I had the space to tell you
More, I'd sing something about that sweetest
Drink, no quantity of which could ever
End my thirst, but because the pages meant
For this canto are already filled, my art prevents me,
Affirming limits I am forced to meet.
[tr. Raffel (2010)]

Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possibly can. You will get an enormous reward. You will have created something.

Everything passes. --
Only robust art is eternal.
The bust outlives the city.

And the simple coin
Unearthed by a peasant
Reveals the image of an emperor.
[Source]

All passes, Art alone
Enduring stays to us;
The Bust outlasts the throne, --
The Coin, Tiberius.
[Austin Dobson, "Ars Victrix" (1876), in imitation]

Everything passes -- Robust art
Alone is eternal.
The bust
Survives the city.
[Source]

Everything disappears -- Robust art
   alone is eternal:
      The Bust survives the city.
[Source]

Everything passes away. -- Robust Art
   Alone has eternity;
      The bust
   Survives the city.
[Source]

• "A painting in a museum hears more ridiculous opinions than anything else in the world."
• "What hears the most stupid remarks in the world is perhaps a painting in a museum." [Source]
• "Perhaps what hears the most nonsense in the world is a museum painting." [Source]

In art as in lovemaking, heartfelt ineptitude has its appeal and so does heartless skill, but what you want is passionate virtuosity.

Heartfelt ineptitude has its appeal, Dunyazade; so does heartless skill. But what you want is passionate virtuosity.

For me, the work is an absolute necessity. I cannot put it off; I don't care for anything else; that is to say, the pleasure in something else ceases at once, and I become melancholy when I cannot go on with my work. I feel then as the weaver does when he sees that his threads have got tangled, the pattern he had on the loom has gone to the deuce, and his exertion and deliberation are lost.
[In I. & J. Stone, ed., Dear Theo: the Autobiography of Vincent Van Gogh (1995)]

The physician can bury his mistakes, but the architect can only advise his clients to plant vines -- so they should go as far as possible from home to build their first buildings.

You think your pain and your heartbreak are unprecedented in the history of the world, but then you read. It was Dostoevsky and Dickens who taught me that the things that tormented me most were the very things that connected me with all the people who were alive, or who had ever been alive. Only if we face these open wounds in ourselves can we understand them in other people. An artist is a sort of emotional or spiritual historian.
[Interview with Jane Howard, Life Magazine (24 May 1963)]

You think your pain and your heartbreak are unprecedented in the history of the world, but then you read. It was books that taught me that the things that tormented me most were the very things that connected me with all the people who were alive, or who had ever been alive.
["James Baldwin Recalls His Childhood," quoting from a television program, New York Times (31 May 1964)]

God manifests himself to us in the first degree through the life of the universe, and in the second through the thought of man. The second manifestation is not less holy than the first. The first is named Nature, the second is named Art. Hence this reality: the poet is a priest.
[tr. Baillot (1864)]

The most beautiful experience we can have is the mysterious. It is the fundamental emotion that stands at the cradle of true art and true science. Whoever does not know it and can no longer wonder, no longer marvel, is as good as dead, and his eyes are dimmed. It was the experience of mystery -- even if mixed with fear -- that engendered religion. A knowledge of the existence of something we cannot penetrate, our perceptions of the profoundest reason and the most radiant beauty, which only in their most primitive forms are accessible to our minds: it is this knowledge and this emotion that constitute true religiosity. In this sense, and only this sense, I am a deeply religious man.

— "The World As I See It [Mein Weltbild]" [tr. Bargmann (1954)]

The fairest thing we can experience is the mysterious. It is the fundamental emotion which stands at the cradle of true art and true science. He who knows it not and can no longer wonder, no longer feel amazement, is as good as dead, a snuffed-out candle. It was the experience of mystery -- even if mixed with fear -- that engendered religion. A knowledge of the existence of something we cannot penetrate, of the manifestations of the profoundest reason and the most radiant beauty, which are only accessible to our reason in their most elementary forms -- it is this knowledge and this emotion that constitute the truly religious attitude; in this sense, and in this alone, I am a deeply religious man.

— "The World As I See It [Mein Weltbild]" [tr. Harris (1934)]

The most beautiful and deepest experience a man can have is the sense of the mysterious. It is the underlying principle of religion as well as all serious endeavor in art and science. He who never had this experience seems to me, if not dead, then at least blind. To sense that behind anything that can be experienced there is a something that our mind cannot grasp and whose beauty and sublimity reaches us only indirectly and as a feeble reflection, this is religiousness. In this sense I am religious.

[Das Schönste und Tiefste, was der Mensch erleben kann, ist das Gefühl des Geheimnisvollen. Es liegt der Religion sowie allem tieferen Streben in Kunst und Wissenschaft zugrunde. Wer dies nicht erlebt hat, erscheint mir, wenn nicht wie ein Toter, so doch wie ein Blinder. Zu empfinden, dass hinter dem Erlebbaren ein für unseren Geist Unerreichbares verborgen sei, dessen Schönheit und Erhabenheit uns nur mittelbar und in schwachem Widerschein erreicht, das ist Religiosität. In diesem Sinne bin ich religiös.]

— Variant in "My Credo [Mein Glaubensbekenntnis]" (Aug 1932)

Paraphrased over a long period of time (and still attributed to Reynolds) as: "There is no expedient to which a man will not resort to avoid the real labor of thinking."

The lecture was later described as the Twelfth Discourse in a 1797 collection of Reynolds' works.

Often attributed to Thomas Edison. More information here.