The Thing about Plato's cave is not that normal people are actually living like shadow puppets. It's that guys like Plato prefer to see it that way because they can't really get into it. If you don't understand how to interact with normal life then you wind up creating a higher plane to imagine within. Or perhaps that's chicken and egg in reverse. Perhaps your imagination is so strong that there's nothing left in your brainpower for apprehending normal physical & social interactions. But whichever one sparks the other first, these two trends reinforce one another after a while and spiral ever stronger.
So how does this really begin? It might have something to do with words. Words are algebraic. Language is the abstraction of things into symbols. In algebra we let X stand for a number and then having abstracted the concept of value we begin talking about X without reference to any particular number. For certain minds, all of language has this same power. The potential for variability of language is sometimes called irony or ambiguity but what it is is abstract variability. It's algebraic.
So, that helps explain Plato and people like him. Maybe it happens whenever a child is profoundly immersed in literature from an early age and happens to find it enjoyable. But being attracted to a story world which stands apart from the real world is only one part of the captivating mystique. Simply in the way that I can use the word tree and have that simple signifier conjure things inside your mind - images, experiences, perhaps even sounds and smells - memories of places you've been and sights you've overlooked. If focused upon strongly enough, the word tree has a magical power to conjure up an imaginary world inside your head. ...and how can reality ever compete?
But it is words especially that seem to have power. Although other things can bring the same effect at stimulating imagination and memory, they are far less common. I can walk in the park and stare at one tree and let it remind me of other countries or imaginary trees but there is always a particular tree physically visibly before me in front of which I am presently sitting. That cannot have the power of "tree ". And so there is something fascinating about words. And just as some children become captivated by the motion of a ball or the appearance of pretty things or by making other children smile or even cry, there were some of us who became captivated very early on with the power of words. This can draw you in as fully as anything else.
So eventually you get guys like Plato('s Socrates) who see the entire world as insufficient to account for the potential of words. It's a complete fabrication when they develop this concept about a higher plane of pure ideas but it isn't an accident. What they came up with was the natural progression of focusing on words and finding out what words can do. Let me say that again. The "idea plane" (or something very much like it) was every bit as inevitable among brainy wordsmiths as the Super Bowl (or something very much like it) was inevitable once guys began playing rugby.
Eventually... What this leads to is simultaneously a great benefit and a tremendous drawback for Christian theology, because this higher plane of being seems to mimic the higher plane of God...
Jesus is truly deeply and metaphorically the Word, not in human ideology, but Jesus is the actual signifier of God as a word is an actual signifier of things... This does not mean that God is a higher form of human intellect, "the Word". No, this means that God became communicable by incarnating in Jesus. It does not mean Jesus is the words that God would speak to us, or thoughts that God would speak - although Jesus may be those things - but it means Jesus himself *IS* the speech-like effort of God to explain himself to human beings. He is what best references, signifies, represents, or stands for God. "The Word" is the opening metaphor of one idea that stays consistently expressed through the rest of the chapter. As one translator rendered, "He came to show us what God was like."
And so, whether we think about Logos or Eidos or simply higher levels of thinking in general, we do well to remember that words should always, in some way or another, point us back to a real experience of things...
Experience always trumps. Period.