Duality or non duality ?
The mystics say: everything is just one thing, ie " Non Duality" where as in the land of opposites(Duality) everything has it's opposites hot/cold, feast/famine, beautiful/ugly, so on and so on....
I think perhaps everything is just a dance between opposites ying/jang and finding the Tao to live better or in harmony with and not against ,, so many ways to approach life anyway I think those that probed the mind deeply in ancient times where on to something and non duality may have been it.