"I wanted it to be totally in character of what’s going on with the lyrics and a summing up of my guitar playing for that particular song. What I’d do is just limber up and then, okay, put the red light on. And again, those solos weren’t done over hours and hours. They were pretty much improvised. They weren’t worked out note for note. Never. The solos were always: take a deep breath and go for it! For the spontaneity. I might have worked out how I might start it off. But that’s it."
January 1, 1970
https://en.wikiquote.org/wiki/Led_Zeppelin