Thank you for your input Tigerjaw, I was thinking along the same lines when I read the poem. It reminds me of a passage from Coleridge's Rime of the Ancient Mariner...
Like one who, on a lonely road,
Doth walk in fear and dread,
And, having once turned round, walks on,
And turns no mare his head;
Because he knows a frightful fiend
Doth close behind him tread
Humans tend to always look behind them; our past sins and failures prevent us from living in the moment as animals do because we're always looking back at life, or dreading looking back because of what is there.