Lyric discussion by txfilmguy1 

Equating this song with the myth of Led Zeppelin's pact requires a lot of imagination. The pact, along with most everything else found in "Hammer of the Gods" is simply myth... creating legends out of merely talented men. Were Black Sabbath satanists? No, but misleading their audience into thinking they were was a boon to publicity. Truth is the legend of the pact was lifted from the song "Crossroads," which the guys were all fans of.

On to the meaning of the song...

It's pretty cut-and-dry. He loves life on the road. Even the monotonous drone of the tires and the weary rocking of the bus. It allows him to become interspective. His imagination is piqued by the myriad scenes passing by his windows and this allows him the freedom to create songs. His lover, on the other hand, sits and home and stares at the mirror, waiting for the tour to be over. It is a doomed relationship. She waits for him to come home, and then he waits to hit the road. So while he is out on tour, she decides to leave him. "There is no turning back... on the run." He doesn't like that she is leaving him, but such is life on the road.

As for the title... maybe he was in the bathroom on the bus staring at his new creation while writing this song. No idea there.

such a great explanation, excellent !

@txfilmguy1 The bathroom explanation may not be far fetched. The only well known reference to "Big Log" is the old joke about the three ducks that stayed the night in a hotel where the only space for them was in the bathroom. Two stayed in the bathtub, but the third had to stay in the toilet. The two ducks in the tub said they had a good night's sleep. The duck in the toilet said that at first he was sleeping well, but in the middle of the night, it thundered, then rained, then a BIG...

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