“From infancy on, we are all spies; the shame is not this but that the secrets to be discovered are so paltry and few.”

Tory MP deletes tweet accusing Jeremy Corbyn of 'selling British secrets to Communist spies
Source: https://www.theguardian.com/politics/2018/feb/24/ben-bradley-apologises-unreservedly-for-corbyn-spy-claims

In response to a question from an audience member
2004 speech to the Supreme Cultural Revolution Council

As quoted in Hugs for Girlfriends : Stories, Sayings, and Scriptures to Encourage and Inspire (2001) by Philis Boultinghouse and LeAnn Weiss, p. 7; there seem to be no published sources available for this statement prior to 2001.
Disputed

My Reviewers Reviewed (lecture from June 27, 1877, San Francisco, CA)
Context: The earth, rotating at the rate of one thousand miles an hour, was stopped. The motion of this vast globe would have instantly been changed into heat. It has been calculated by one of the greatest scientists of the present day that to stop the earth would generate as much heat as could be produced by burning a world as large as this of solid coal. And yet, all this force was expended for the paltry purpose of defeating a few poor barbarians. The employment of so much force for the accomplishment of so insignificant an object would be as useless as bringing all the intellect of a great man to bear in answering the arguments of the clergymen of San Francisco.

[Haggard, Ted, Letters from Home, Regal Books, March 2003, p. 18, ISBN 0830730583]

Source: Now, Discover Your Strengths (2001), p. 21

Variant: What you learn today, for no reason at all, will help you discover all the wonderful secrets of tomorrow.
Source: The Phantom Tollbooth

Source: The Secret Oral Teachings in the Tibetan Buddhist Sects (1964)

Nixon, Haldeman, and Ziegler, 4:03 P.M., Oval Office Conversation #537-4; cassette #876 (5 July 1971)
1970s