There's an anecdote that I retail fairly often in spoken form but almost never in writing — because I like to cite my sources when writing, and I can't for the life of me figure this one out. The story is usually attributed to George Bernard Shaw or Mark Twain, and generally takes the form that the great author closed a letter (or appended a postscript) with a sentence something like:
I apologize for sending such a long letter; I did not have time to write a short one.
Google finds me many, many instances of people "quoting" variants of this sentence, and attributing it to Shaw or Twain. Or Blaise Pascal. Or Dr. Johnson. Or to Oliver Wendell Holmes, Jr. (who is suppose to have prepended it to his reading an opinion from the bench while serving on the Massachusetts Supreme Judicial Court). Or to "nineteenth-century writer Madame de Staël" (Which is, I think, most probably the correct attribution. Mme de Staël is an order of magnitude less famous than any of the other attributees, and people who remember a pithy remark but not its source are, I should expect, more likely to attribute it to someone famous. Also, while the number of variations on the phrase may be explained by the folk process, the variety would make even more sense if the original was not English, and hence all the variants trace their roots to variant translations. Still, I have been unable to chase it to ground.)
I don't suppose anyone has ever actually encountered this phrase in its original context, and could provide an actual citation? Surely my social network must include someone who's into late-eighteenth and early nineteenth century French literature....