“The difference between an optimist and a pessimist is that the pessimist is (generally/usually) better informed” is an old joke that can apply to any type of information, such as political information or financial information. American playwright and politician Clare Boothe Luce (1903-1987) is often credited with saying this, but there is no evidence that she said it first. In a 1986 book, Luce was credited with saying, “I found in my own experience that the real difference between pessimists and optimists is that the pessimists are generally better informed. “
 
“What’s the difference between an optimist and a pessimist?” was said to be “the current Budapest joke” in 1969. Several 1969 citations from Hungary indicate that the joke was at least popularized (if not coined) by Hungary under communism.
 
“A pessimist is a well-informed optimist” is another form of the same saying.
 
 
30 October 1969, The Times-Picayune (New Orleans, LA), “The Lyons Den” by Leonard Lyons, sec. 6, pg. 3, col. 1:
Lang told him this story from his native Hungary: Q: “What’s the difference between an optimist and a pessimist?”
 
Answer: “Nothing. Except the pessimist is better informed.”
   
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NHQ; the New Hungarian Quarterly
Volume 10, Part 2
1969
Pg. 130:
They started to tell me the current Budapest joke. “What’s the difference between an optimist and a pessimist?” I know. A pessimist is better informed.
 
Google News Archive
5 May 1970, Reading (PA) Eagle, pg. 22, col. 5:
Prof. George Quayles insists that the only difference between a pessimist and an optimist these days is that a pessimist is obviously better informed.
 
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Britain:
A Future that Works
By Bernard D. Nossiter
Boston, MA: Houghton Mifflin
1978
Pg. 193:
A Hungarian proverb holds that the difference between an optimist and a pessimist is that the pessimist is better informed.
 
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Thinking about East/West:
A Conference of the Committee for the Free World
By Elliott Abrams, Committee for the Free World, et al.
New York, NY: Orwell
1986
Pg. 124:
Clare Booth Luce
M. Revel, I found in my own experience that the real difference between pessimists and optimists is that the pessimists are generally better informed.
 
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Finding Answers:
The Essential Guide to Gathering Information in Canada
By Dean Tudor
Toronto, Ontario: McClelland & Stewart
1993
Pg. 167:
The only difference between an optimist and a pessimist is that the pessimist is better informed.—old joke
 
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Dutch: A Memoir of Ronald Reagan
By Edmund Morris
New York, NY: Modern Library (Random House)
1999
Pg. 285:
“The only difference between an optimist and a pessimist,” Clare Boothe Luce used to say, “is that a pessimist is usually better informed.”
 
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Energy for a Sustainable World
By Vincenzo Balzani and Nicola Armaroli
Hoboken, NJ: John Wiley & Sons
2010
Pg. ?:
An old Italian proverb says that the only difference between an optimist and a pessimist is that the latter is better informed.