Past, present and future are the three heads of Cerberus, who blocks our path. If we recognize the false nature the extra heads all that remains is a friendly companion who exists along side us in the now. The past is memories of what used to be now, the future is expectations of what will be now, but technically there has only ever been the eternal ‘now’. Only the eternal may traverse the underworld.
This image from a previous post helps explain this notion.