When Jung was immersed in his study of the symbolism of the fish in Christianity, alchemy and world mythology, the theme started leaping at him in everyday life. On April 1, 1949, he made some notes about an ancient inscription describing a man whose bottom half was a fish. At lunch that day, he was served fish. In the conversation, there was talk of the custom of making an "April fish" - a European term for "April fool" - of someone.
In the afternoon, a former patient of Jung's, whom he had not seen for months, arrived at his house and displayed him some "impressive" pictures of fish. That evening, Jung was shown embroidery that featured fishy sea monsters. The next day, another former patient he had not seen in a decade recounted a dream in which a large fish swam towards her.
Several months later, mulling over this sequence as an example of the phenomenon he dubbed synchronicity, Jung walked by the lake near his house, returning to the same spot several times. The last time he repeated this loop, he found a fish a foot long lying on top of the sea-wall. Jung had seen no one else on the lake shore that morning. While the fish might have been dropped by a bird, its appearance seemed to him quite magical, part of a "run of chance" in which more than "chance" seemed to be at play