If there appears to be something outside (external world), there must always be someone (internal world) to observe it.
These two extremes—the external world and the internal observer—give rise to duality, which is an illusion.
Who is this observer in the illusion? The observer is none other than the self-existence feeling—the sense of "I".
Due to ignorance and distorted vision, the observer believes the object exists independently outside.
As known in physics, when two opposite ends exist (positive and negative charge, north and south pole, particle and anti-particle), interaction arises.
Likewise, the illusion of duality between the external world and the internal observer generates the interaction force—mind power.
This mind power sparks at that very moment as a vibration arising through the sensory functions/process. (See here to understand how the mind spark arises)
When this illusion is penetrated with right vision, realizing that thought itself is merely a vibration, duality dissolves.
The self-existence feeling fades away, revealing that there was never an "I" to begin with.
There is no observer—only the natural sensory function remains, such as seeing without a seer, merely as a process of nature.
The arising of duality is entirely due to ignorance (not knowing the truth), but with right understanding, only the bare sensory function arises in that very moment—free from the illusion of self and the world.
Page: No External World, No Duality: