Necessity of Illusion

We cannot “know” without knowing the “not know”. In the sense, to know something we need to know the condition where something is not also! To have a complete understanding both assertion and negation of that assertion should be known…….meaning to say, that to assert 'oneness' truth we need to know the 'duality/multiplicity' beforehand as well. So it is necessary to be in the world of illusion before you completely see and appreciate the oneness in/of reality.