The world is a drama staged in a dream, which alludes to the Hindu notion of maya. The physical reality is all an illusion. We want to pierce through that veil. What should the yogi have to fear? Trees, plants, and all that is inside and outside is he himself. So this is an idea that we get very clearly from the Upanishads. Any notion of duality, of me being different from you, or even one versus God, it's all an illusion.