Because the song was actually written in 1955 for two banjos.
Long before the movie "Deliverance" came out in 1972. "Deliverance"
just made it more famous.
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The film called Deliverance was directed by John Boorman.
The thriller was released in July 1972.
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The movie Deliverance was filmed on the Chatooga River which
borders Georgia and South Carolina.