It has to do with "the law of attraction", "active visualization", call it what you will. A stream of books, films, cd's, have come out in recent years -"What the Bleep Do We Know", "The Secret", "The Law of Attraction", to name a few - all with basically the same message: laws of physics suggest that when we act, think and feel a certain way, we attract the very thing we are focused on.
When I was a boy, learning to play the guitar, my teachers would get mildly frustrated with me. I would come into the lesson imitating a different player practically every week. I would see their picture on an album cover and copy the way their hands looked (which was rarely attractive), or do my best to sound just like them. And I became really good at it. When I look back on it, "pretending" was my own way of active visualization; I would copy something, and then let my playing adjust to the physical traits I was taking on. Not always brilliant results, but the self-training was extremely valuable.
There are a couple of lessons here, I think. First, embrace a child's enthusiasm to pretend, especially when he/she is pretending with artistic projects. What child do you know who doesn't believe they are a great artist when they show you a crayon drawing?
Secondly, grownups should pretend more. We should give ourselves some regular time to let our imaginations out of the cage and go free.
I have had a saying floating around on my computer desktop for a couple of years now, and I'm finally beginning to realize how powerful and true it is, and rarely easy to do: "Act as Though I Am, and I Will Be".