
“If I can't picture it, I can't understand it.”
Attributed to Einstein by physicist John Archibald Wheeler in John Horgan's article "Profile: Physicist John A. Wheeler, Questioning the 'It from Bit'". Scientific American, pp. 36-37, June 1991. Reprinted here http://www.scientificamerican.com/article.cfm?id=pioneering-physicist-john-wheeler-dies after Wheeler's death.
Attributed in posthumous publications