“The mind that opens to a new idea, Never comes back to its original size.”

Often given as: A mind that is stretched by a new experience can never go back to its old dimensions.
Or: A mind that is stretched by a new idea can never go back to its old dimensions.
Actually by Oliver Wendell Holmes, Senior, from " Autocrat of the Breakfast Table https://books.google.com/books?id=BoQ3AQAAMAAJ&pg=PA502&dq=%22stretched+by+a+new+idea%22&hl=en&sa=X&ved=0ahUKEwidspn60tTJAhVJ1GMKHbt3Bn0Q6AEIHTAA#v=onepage&q=%22stretched%20by%20a%20new%20idea%22&f=false", originally published in The Atlantic, September 1858.
Misattributed

Source: Think Big (1996), p. 224

Epilogue
Novels, Squeeze Me (2020)

Discours d'ouverture, congrès de la paix http://fr.wikisource.org/wiki/Congr%C3%A8s_de_la_Paix_1849, [Opening address, Peace Congress], Paris (21 August 1849); published in Actes et paroles - Avant l'exil (1875)
Context: A day will come when there will be no battlefields, but markets opening to commerce and minds opening to ideas. A day will come when the bullets and bombs are replaced by votes, by universal suffrage, by the venerable arbitration of a great supreme senate which will be to Europe what Parliament is to England, the Diet to Germany, and the Legislative Assembly to France.
A day will come when a cannon will be a museum-piece, as instruments of torture are today. And we will be amazed to think that these things once existed!
A day will come when we shall see those two immense groups, the United States of America and the United States of Europe, facing one another, stretching out their hands across the sea, exchanging their products, their arts, their works of genius, clearing up the globe, making deserts fruitful, ameliorating creation under the eyes of the Creator, and joining together, to reap the well-being of all, these two infinite forces, the fraternity of men and the power of God.

The Autocrat of the Breakfast Table (1858)

Source: Brightness Reef (1995), Ch. 25
Context: It's how creativity works. Especially in humans. For every good idea, ten thousand idiotic ones must first be posed, sifted, tried out, and discarded. A mind that's afraid to toy with the ridiculous will never come up with the brilliantly original.

No Idea's Original
On Albums, The Lost Tapes (2002)

Think Like an Artist (2015)