That's one of the reasons you'd put your best song on side A, song 1 and your 2nd best song on side B, song 1 - you got the most detail on the outside track. I remember seeing an interview with Led Zeppelin quite a few years back where they were claiming they knew they'd have a smash hit with Stairway to Heaven. Which was funny, because I remembered then seeing an interview several years before where they said it was a track they never thought was going to go anywhere.

Which is it? It's track position - 4th track on the A side, i.e. the last track, tells you how important they thought it was. Which is to say, it was a "throwaway" track that made it big. It happens.

The other odd thing about that album is "When the Levee Breaks" is considered to be the 2nd-most popular song off of the album and it too was the last track on the B side.

What this tells me is the album's producer, one Jimmy Page, was out of touch with what Led Zeppelin fans liked most. Based off the sound of the next album, Houses of the Holy, I'd say Mr. Page got the message loud and clear.