The thinking is seeing itself as something passing, in constant change, and therefore it produces the thinker as a constant entity, as separate from the thought, different from it.
Then the thinker works in on the thought, divides, accepts and denies, accentuates and excludes.
But all the time there is only the thinking.
No more than we can place ourselves outside life, no more can the thinker place himself outside the thought.
It is an illusion, a self-deceit.