“Imagine an underground chamber, like a cave with an entrance open to the daylight... In this chamber are men who have been prisoners there since they were children, their legs and necks being so fastened that they can only look straight ahead of them and cannot turn their heads. Behind them and above them a fire is burning, and between the fire and the prisoners... a curtain-wall has been built, like the screen at puppet shows between the operators and their audience… Do you think our prisoners could see anything of themselves or their fellows except the shadows thrown by the fire on the wall of the cave opposite them? ... Would they not assume that the shadows they saw were real things? ... And if the wall of their prison opposite them reflected sound, don’t you think that they would suppose whenever one of the passers-by on the road spoke, that the voice belonged to the shadow passing before them? Suppose one of them... were suddenly compelled to stand up and turn his head and look and walk towards the fire... he would be too dazzled to see properly the objects of which he used to see the shadows. So if he was told what he used to see was mere illusion and that he was now nearer reality and seeing more correctly, don’t you think he would be at a loss, and think that what he used to see was more real than the object now being pointed out to him?”
Plato c.380 B.C. From Book 7 of The Republic, translated by H.P.D. Lee, Penguin Classics