I myself found a fascinating example of this in Nietzsche’s book Thus Spake Zarathustra, where the author reproduces almost word for word an incident… - Carl Jung

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I myself found a fascinating example of this in Nietzsche’s book Thus Spake Zarathustra, where the author reproduces almost word for word an incident reported in a ship’s log for the year 1686. By sheer chance I had read this seaman’s yarn in a book published about 1835 (half a century before Nietzsche wrote); and when I found the similar passage in Thus Spake Zarathustra, I was struck by its peculiar style, which was different from Nietzsche’s usual language. I was convinced that Nietzsche must also have seen the old book, though he made no reference to it. I wrote to his sister, who was still alive, and she confirmed that she and her brother had in fact read the book together when he was 11 years old. I think, from the context, it is inconceivable that Nietzsche had any idea that he was plagiarizing this story. I believe that fifty years later it has unexpectedly slipped into focus in his conscious mind.