“There is no such uncertainty as a sure thing.”
Reported as attributed to Burns but unverified in Suzy Platt (ed.), Respectfully Quoted: A Dictionary of Quotations Requested from the Congressional Research Service (Washington, DC : Library of Congress 1989) http://www.bartleby.com/73/172.html
Disputed
Source: Collected Poems of Robert Burns
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Robert Burns 114
Scottish poet and lyricist 1759–1796Related quotes
Ikujiro Nonaka (1991), "The Knowledge-Creating Company", Harvard Business Review 69 (6 Nov-Dec): 96–104

“The most precious thing in life is its uncertainty.”
Essays in Idleness (1967 Columbia University Press, Trns: Donald Keene)
Context: If man were never to fade away like the dews of Adashino never to vanish like the smoke over Toribeyama, but lingered on forever in the world, how things would lose their power to move us! The most precious thing in life is its uncertainty. Consider living creatures- none lives so long a man. The May fly waits not for the evening, the summer cicada knows neither spring nor autumn. What a wonderfully unhurried feeling it is to live even even a single year in perfect serenity.

“Uncertainty and expectation are the joys of life. Security is an insipid thing.”
Act IV, scene xx
Love for Love (1695)

“I have known that thing the Greeks knew not – uncertainty.”
"The Lottery in Babylon"; tr. Andrew Hurley, Collected Fictions (1998)
The Garden of Forking Paths (1942)
Variant: I have known uncertainty: a state unknown to the Greeks.
“Uncertainty is a personal matter; it is not the uncertainty but your uncertainty.”
1. Introduction. p. 1.
Understanding Uncertainty (2006)

“Knowledge would be fatal. It is the uncertainty that charms one. A mist makes things wonderful.”
Source: The Picture of Dorian Gray

Learning to Fly: A Memoir of Hanging On and Letting Go (New York: Touchstone, 2015), pp. 83 https://books.google.it/books?id=IIDRCgAAQBAJ&pg=PA83-84.

"Unlikely heir who saved the family jewels" http://www.ft.com/cms/s/0/0693507a-4830-11e0-b323-00144feab49a.html#axzz1GZU7VVRA, Financial Times, 03-06-11