Dreams and Visualisation

This morning I was wondering why my dreams can be almost indistinguishable from reality, yet when I visualise something, it lacks vividness and clarity. Not only that but I often get distracted when I visualise something - I vanish down a stream of consciously only to snap out of it a few seconds later and realise that I had lost focus.

To me this implies that we have an untapped potential for crystal-clear imagery in our heads that we could somehow unlock. I wonder what the secret is? Imagine if your imagination could be as clear as a lucid dream!