An aspect of what Krishnaji says might be simple.
It seems when you attend, thought cannot be, there is observer aspect but thought ends as it seems focus can only be observer or observed at any one time. Mind has great difficulty being both, it becomes extremely taxing for the brain.
They are merely 2 aspects of the same process.
This is maybe why we commonly consider there is a separate observer from the observed as we generally switch between them almost unconsciously as we don't feel much importance in this.
Just as an example when you are angry you have total focus on anger so there is no division in the mind. When you look back the next day it is an observer looking at what was, a division.
Attention cannot be the aspects we consider observer and the observed at the same time.
There is a shift in focus between thinking (absorbs you) which takes focus away from being the observer.
They seem like 2 aspects of same mind.
Just as you cannot drive 2 cars at once, but the switching seems, like inconsequential gear changes..
This is maybe why we commonly consider there is a separate observer from the observed.
Observer being observed is hidden from you. I am getting some kind of feeling the mind hides aspects of its operation away when it comes under the microscope of attention.
That's interesting and tricky of it isn't it.
Whilst the mind acts as observer, the observed is awareness of senses, and cannot be thought.
I don't really know if this is much use to see though. It might be somehow useful to see that the mind is hiding aspects of itself making self and observer and observed more difficult to understand and see or in case of self, see through.