His "MU" was a blow aimed at breaking or untying the attachment even at the teaching itself; the essence is non-attachment. All human troubles and sufferings, without exception, are due to attachment. Even attachment to the idea of non-attachment is the attachment. It transcends the relative world and gains the free and independent world of satori.
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Our life is always attached to the relative: the "is" and the "is not," "good" and "bad," "right" and "wrong". But life itself constantly changing: the condition of society changes, right and wrong changes. Every situation is different according to the time and place. Static concepts are not appropriate to life, but the concepts like faith, hope, and love are; because they grow and evolve.
The tao that can be told is not the eternal Tao The name that can be named is not the eternal Name. The unnamable is the eternally real. Naming is the origin of all particular things. Free from desire, you realize the mystery. Caught in desire, you see only the manifestations. Yet mystery and manifestations arise from the same source. This source is called darkness. Darkness within darkness. The gateway to all understanding. Tao The Ching Chapter 1