"This is the verdict: Light has come into the world, but people loved darkness instead of light because their deeds were evil" (Jn 3:19).
Chained since birth (like the man born blind in John 9). Plato's allegory is of prisoners chained since birth deep inside a cave. They face a blank wall and can only see shadows cast on it by people, animals and objects (illuminated by a fire they can't see). For these prisoners, the shadows are reality, their only reality; it's all they've ever known, as they have never seen the light.