My heavy-metal-loving pal and I do have some overlap in musical interests. ‘What Is And What Should Never Be’ is off Led Zeppelin’s awe-inspiring 1969 long player Led Zeppelin II. Written by Jimmy Page and Robert Plant, this track seems bipolar; it switches between the folky one minute and axe-wielding the next. Plant was reflecting upon a romance he’d had with his wife’s younger sister (allegedly). Page was hammering his soon-to-become trademark Gibson Les Paul. The band embraced the contemporaneous technology to make it all knit together… stereo channels, phased-out vocals and something strong to suppress John Bonham’s thunderous power.