Guitarist Tony Iommi has revisited the origins of Black Sabbath's "Symptom of the Universe," a track widely regarded as home to one of the greatest riffs in metal. Speaking to Hammer magazine, Iommi admitted he could not recall exactly when the song was written, but explained that it grew out of his determination to avoid copying anyone else, including sounds he himself had already established with Sabbath. The riff is credited with helping lay the groundwork for thrash metal, making its creation notable beyond the band's own catalogue.

Released on Black Sabbath's 1975 album "Sabotage," the song was written by Iommi and bassist Geezer Butler. Iommi described deliberately competing only with himself, experimenting with tunings and amp settings while avoiding listening to other guitarists in case he unconsciously borrowed their ideas. He also revealed that the track's unexpected shift into jazzier territory midway through was unplanned, arising simply from the band jamming together, with Butler, drummer Bill Ward and singer Ozzy Osbourne following his lead into unpredictable musical territory.