“Paranoid” was written literally as a postscript. They needed a three minute song to complete the record. Tony Iommi came up with the riff, Butler wrote the lyrics quickly, and Ozzy Osbourne was reading them almost while he was singing them. There is also the even more compressed version of the story, that Iommi came up with the basic riff in four minutes and that the whole song was written and recorded in about twenty to twenty five minutes. Iommi himself has said to Songfacts that the song was written simply as a filler for the album and was never intended to be anything more. It became a single only because it was a short track, unlike their longer and heavier compositions. And in the end it became exactly what it became. So much so that people back then knew them mainly through “Paranoid.”