You wanted to know about the double.  It begins in dreams.  But then you asked, ‘What is the double?’  And I said the double is the self.  The self dreams the double.  That should be simple, except that there is nothing simple about us.  Perhaps the ordinary dreams of the self are simple, but that doesn’t mean that the self is simple.  Once it has learned to dream the double, the self arrives at this weird crossroad and a moment comes when one realizes that it is the double who dreams the self.
  - Don Juan, in Tales of Power, by Carlos Castaneda, p81

In this chapter I introduce the art and science of lucid dreaming, and the psychological implications of a window into the unconscious. I explain the value of lucid dreaming to knowing this part of ones self. Note that the dream body, or avatar, does not ever wake up, it is the dreamer who wakes up. In lucid dreaming, one is first aware he is dreaming, but as a helpless observer or participant.  Next, the dreamer is not only aware, but is able to influence the plot and even draw characters in.  Then, one learns to set up dreaming to explore a specific scenario and seem have dialogue with specific people, dead or alive, or receive information from dream-character masters or angels.  The motivation to master lucid dreaming is to open a window into the unconscious, obscured by the inability to remember dreams, and even if remembered, the inability to use them as a tool of self-analysis. The underlying purpose of this activity is not, as Don Juan said, to learn a new description, but rather to arrive at the totality of oneself.