The object determines the subject
(The beauty of the following is that it's not a theory, you can try it by yourself)
The observed object determines the observing subject.
What you observe can not be you. Once you observe it and accept it, your identification with the object breaks and the "I", the subject, is reduced to being what it was before minus the object.
This is the art of awareness, To observe more and more, to find more and more things you were resisting and thus suppressing and thus not observing and thus subconsciously being identified with. By doing this, "you", the subject becomes less and less until you are not and then there is no duality of subject-object anymore.
On the way, you will peel in that way the physical world including your body, the senses that sense this world and body and the sensor, you will peel your various emotions and the feeler of the emotions, your various analytical processes and thoughts and the thinker and all other aspects of your mind and the mind itself as subject that are associated with dealing with objects, mental as well as physical, "internal" as well as "external".
Given your current "fat" "I" containing objects you are identified with, you have no many choices other than observing in order to peel the identified objects, in order to minimize into being, into non-duality.
Intellectual inquiry can nor help you in this path to non-duality since you need the mind for that and the mind is also an object you must include in the list of things you must peel. Once you peel it, you can only observe it.
(The beauty of the above is that it's not a theory, you can try it by yourself)