Quotes from book
Expanded Universe

Name: Expanded Universe
Author: Robert A. Heinlein

Expanded Universe, The New Worlds of Robert A. Heinlein is a 1980 collection of stories and essays by American writer Robert A. Heinlein. The trade paperback 1981 edition lists the subtitle under other Heinlein books as More Worlds of Robert A. Heinlein because the contents subsume the 1966 Ace Books collection, The Worlds of Robert A. Heinlein. The current volume is dedicated to William Targ.

“The 3-legged stool of understanding is held up by history, languages, and mathematics. Equipped with those three you can learn anything you want to learn. But if you lack any one of them you are just another ignorant peasant with dung on your boots.”

Robert A. Heinlein book Expanded Universe

Source: "The Happy Days Ahead" in Expanded Universe (1980)
Context: I started clipping and filing by categories on trends as early as 1930 and my "youngest" file was started in 1945.
Span of time is important; the 3-legged stool of understanding is held up by history, languages, and mathematics. Equipped with these three you can learn anything you want to learn. But if you lack any one of them you are just another ignorant peasant with dung on your boots.