Well, lets go directly to Joseph Campbell, who says something like,
"We must be willing to get rid of the life we've planned, so as to have the life that is waiting for us. The old skin has to be shed before the new one can come."
In other words, it's about losing the old self and becoming the new self - it's about transformation.
The hero's journey is the basis of all successful screenplays and stories; we have discovered more than 2000+ stages you need to know about - learn more about it at http://www.clickok.co.uk/index4.html