"I think there is a world market for maybe five computers"

Thomas J Watson - 1943?
From Wikipedia

Although Watson is well known for his alleged 1943 statement: "I think there is a world market for maybe five computers," there is no evidence he ever made it. The author Kevin Maney tried to find the origin of the quote, but has been unable to locate any speeches or documents of Watson's that contain this, nor are the words present in any contemporary articles about IBM. The earliest known citation is from 1986 on Usenet in the signature of a poster from Convex Computer Corporation as "I think there is a world market for about five computers" Remark attributed to Thomas J. Watson (Chairman of the Board of International Business Machines), 1943. Another early article source (May 15, 1985) is a column by Neil Morgan, a San Diego Evening Tribune writer who wrote: 'Forrest Shumway, chairman of The Signal Cos., doesn't make predictions. His role model is Tom Watson, then IBM chairman, who said in 1958: "I think there is a world market for about five computers."'. However one of the very first quotes can be found in a book "The Experts Speak" written by Christopher Cerf and Victor S. Navasky in 1984. But Cerf and Navasky just quote from a book written by Morgan and Langford, "Facts and Fallacies". However all these early quotes are questioned by Eric Weiss, an Editor of the Annals of the History of Computing in ACS letters in 1985.[8]

However, in 1985 the story was discussed on Usenet (in net.misc), without Watson's name being attached. The original discussion has not survived, but an explanation has; it attributes a very similar quote to the Cambridge mathematician Professor Douglas Hartree, around 1951:

I went to see Professor Douglas Hartree, who had built the first differential analyzers in England and had more experience in using these very specialized computers than anyone else. He told me that, in his opinion, all the calculations that would ever be needed in this country could be done on the three digital computers which were then being built one in Cambridge, one in Teddington, and one in Manchester. No one else, he said, would ever need machines of their own, or would be able to afford to buy them.
(quotation from an article by Lord Bowden; American Scientist vol 58 (1970) pp 4353); cited on Usenet.[9]

The misquote is itself often misquoted, with fifty computers instead of five.

Interestingly, since the quote is typically used to demonstrate the fallacy of predictions, if Watson did make such as prediction in 1943, then, as Gordon Bell pointed out in his ACM 50 years celebration keynote, it would have held true for some ten years.[10]