Conversation

They are polar opposites, in the same way that left and right are polar opposites—but it does not make sense to talk about left without right. Thus, though explicitly antithetically different, they are implicitly inseparable.
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Your left hand is not your right hand, but they are parts of the same body, and in that sense they are one. Without the body uniting them, neirher could exist. In this sense nirvana is samsara.
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Replying to and
consciousness which ignores the unity and inseparability of all polarities by focusing on only one at a time at the cost of ignoring the other. This is called 'avidya' in Sanskrit. The apex point of any spiritual endeavor is to overcome this ignorance.