The book: God Bless You, Mr. Rosewater. By Kurt Vonnegut. 1965.
The book within the book (one of several, actually): Pan-Galactic Three-Day Pass. By Kilgore Trout. Publishing date indeterminate.
Quotation from Pan-Galactic:
"Sergeant Boyle was an Earthling. He was the only Earthling on the expedition. In fact, he was the only creature from the Milky Way. The other members were from all over the place. The expedition was a joint effort supported by about two hundred galaxies. Boyle wasn't a technician. He was an English teacher. The thing was that Earth was the only place in the whole known Universe where language was used. It was a unique Earthling invention. Everybody used mental telepathy, so Earthlings could get pretty good jobs as language teachers just about anywhere they went.
The reason creatures wanted to use language instead of mental telepathy was that they found out they could get so much more done with language. Language made them so much more active. Mental telepathy, with everybody constantly telling everybody everything, produced a sort of generalized indifference to all information. But language, with its slow, narrow meanings, made it possible to think about one thing at a time -"
[p.249, of Rosewater]
Is that not a terrifyingly uncanny allegory for technology, communication, and changing modes of thought in the present day? "With everybody constantly telling everybody everything, produced a sort of generalized indifference to all information" - the infinite word & image flows of Wikipedia, Twitter, Facebook, Instagram, what I'm writing on this website right now -- is that not mental telepathy?
What thought is worth more than a moment, if there's to be access to everyone's thoughts - and everything else - all the time?
All I can say is that I am glad for our language's slow narrow meanings and how Vonnegut used them to snap me out of the flow.