Lyric discussion by roserh6 

the song is most definitely a direct reference to advaita vedanta hinduism and buddhism, and many other forms of hinduism/eastern religions.

listen to "pyramid song" where he "jumps in the river" and everything from his past and future is there with him. in siddartha by herman hesse, the protagonist becomes enlightened by listening to the river.

rivers and waterfalls are common images in many eastern beliefs. the syllable om, which encapsulates the entire essence of the ultimate reality or God, is spoken by the river. the river in turn represents the entire universe itself.

the waterfall in this song is no different. thom yorke is only taking the discussion from "pyramid song" a bit deeper. the underlying philosophy of advaita vedanta is that all is one and that we will return to this ultimate source when we die (that is to say when we leave our bodies). "open up and let me in" is referring to this. the material physical world is an illusion, like a dream, a shadow, or a reflection being projected by brahman, the ultimate. the truth is that the eternal consciousness which binds us all is infinite and without time. it is everywhere around us and it is all within us.

the ancient atvaita text the ashtavakra gita talks about renouncing pain and pleasure all together, because these things are all part of maya, which binds us to an existence in absence of the truth. just "be here now" as ram dass would say. this is what the lyrics mean when he says "think about the good times never look back", juxtaposed with, "have ourselves a good time it's nothing at all".

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