“I do not believe that anything really worthwhile will come out of the exploration of the slag heap that constitutes the surface of the moon…Nobody should imagine that the enormous financial budget of NASA implies that astronomy is now well supported.”

As quoted in His Brother's Blood: Speeches and Writings, 1838–64 https://books.google.com/books?id=qMEv8DNXVbIC&pg=PA199 (2004), edited by William Frederick Moore and Jane Ann Moore, p. 199
1860s, Speech to the U.S. House of Representatives (April 1860)

Variant: I sometimes think that people's hearts are like deep wells. Nobody knows what's at the bottom. All you can do is guess from what comes floating to the surface every once in a while.
Source: Blind Willow, Sleeping Woman

Source: Peace Pilgrim: Her Life and Work in Her Own Words (1982), Ch. 2 : My Spiritual Growing Up : My Steps Toward Inner Peace

Source: Summa Theologica (1265–1274), I, q. 25, art. 4

Source: Garrett Reisman (2021) cited in " Bringing Space Down to Earth With Toilets and Toys https://www.space.com/5513-bringing-space-earth-toilets-toys.html" on Space.com, 14 June 2008.

In Vibe magazine cover story, "What Lies Beneath" (Published in 2001) http://www.vibe.com/article/aaliyahs-2001-vibe-cover-story-what-lies-beneath

Rolling Stone, Oct 31 1991, "Right Here, Right Now".

Variant: If you’re always on time, it implies that you never have anything better you should be doing.
Source: Mistborn: The Final Empire

Quoted on Malaysia Kini (February 16, 2016), "Dr M: No surrender in battle against Najib" http://www.malaysiakini.com/news/330557