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is sadness an emotion or simply a reaction to an external stimulus? just like happiness. without knowing what sadness is, how would anyone know when they felt sad? so we feel sad because we have felt happiness before? so sadness is the exact opposite of happiness. but how did we know what we were feeling was happiness in the first place?

why does a baby cry when it enters the world for the first time? everyone around him is so happy! yet when he grows up, grows old, and finally dies, he smiles in his endless sleep, and everyone around him cries.

how exactly do you feel when you 'feel like crying'?