you only can see what you have seen before

the allegory of the cave

And there were people who denied progress, the changes of the times and they withdrew into the caves and wanted nothing to do with all the reflections of the modern world, because it was arrogant and denied the creator, who kept his world constant and without created changes. Exactly as the one had just written his wishes unchangeable in the holy book unchanged for centuries. This old world had its old commandments and, adapted to them, would never, ever change, even thousands of years from now. So you believed.
Secluded in the caves that had eaten their way into the rock in northern Afghanistan over centuries when the valuable blue stone, lapis lazuli, was mined, you were stuck.
So now there were other creatures moving about outside, blinded by the bright daylight. It was almost as if they didn't know what to do. They moved here and there too erratically and hastily. At one point you thought this was their profession, and minutes later they had completely different things in mind. Nothing could keep her busy for a long time, something else was immediately fashionable again.
And so they walked around proudly with the things they had recently got their hands on and enjoyed their appearance and the impression they made on others. They were on the hunt for new superlatives. Some wore valuable jewelry with blue stones, gold and diamonds, others raved about technical highlights, which they practiced for hours every day with nimble fingers. As soon as they were nearly perfect, a completely different handling had to be learned with the next toy and the shine of the old tool quickly faded in the dark. But others sat in front of devices whose only purpose seemed to be to create illusions. These were large screens on which images of the world appeared so alive and moving whereas their viewers' experiences in the real world seemed downright insipid and faded in comparison. For this very reason, those addicted to the illusions could no longer detach themselves from them and were trapped in their addiction.

Allegory of the Cave by Plato (translated from ancient Greek into excerpt from: The State (Politeia)):
After these discussions, I continued, consider now our human disposition before and after its development, with the condition illustrated in the following: Imagine human beings in a cave-like dwelling under the earth, some open to the light and along the whole cave-facing entrance, people whose thighs and necks have been shackled since their youth, so that they sit there motionless and only look ahead, but cannot turn their heads to the left or right because of the shackles; the light for them shines from above and from afar from a fire behind them; between the fire and the prisoners is a crossway above; along this imagine a small wall built, such as the jugglers have in front of the public, over which they show their wonders.
I imagine that, he said.
Now imagine that along this wall people were carrying all sorts of implements that protruded beyond this, including human statues and pictures of other living beings made of wood, stone and all sorts of other materials, while, as was natural, some of the passers-by let their voices be heard, others were silent .
A strange parable, he said, and strange prisoners!
Live likenesses of us! I spoke. Did such captives see anything of themselves and of each other other than the shadows cast by the fire on the wall opposite their faces?
Short excerpt from http://www.pinselpark.de/philosophie/p/platon/staa...
Representation of the Cave Allegory (according to Gottwein)