That "shadow on the wall" is--I have always supposed--a ref. to the Allegory of the Caves, wherein..
'We' sit staring at a wall with ... sometimes moving- pictures displayed. At our backs (all unseen by 'us') is the sunlight(?) streaming through the descending ramp of the long cave-entrance.

Metaphor is Al! ! (~sayeth also Joseph Campbell in that way-back PBS series with Bill Moyers re. "The Power of Myth". Dig it; if you missed it (which I doubt).
Each time I've had the chance to re-view that colloquy, I get more edjumacated--aka: h.t.F. did I miss that little gem?

;^>