You ARE. You know you are. This is undeniable.
This is a certainty of existence.
But what IS that certainty of existence? Why are you so certain? How is it undeniable?
Aren't you certain of your existence because you are obviously present and aware? Isn't this pure subjectivity - "I" - hasn't this "I" always been the basis for all experiences? Hasn't this "I" always been the subject to all objects? Isn't this "I" what is indicated by the word "Awareness"?
Isn't the difficulty in seeing through the "individual self" there because this certainty of existence is SO CERTAIN? And because it's tied up with the objects - "body-mind" - it's impossible to resolve.
This is the exact point of inquiry. How did this certainty of existence, this pure and ever-present subjectivity, this "I", get mixed up with objects?
You have always known "I", yet what "I" IS, is the only issue. Knowing what you are means knowing what "I" IS. Instead of "what am I?" ask "what IS 'I'?"
As the body-mind, this "I" is quite confusing. Yet through neti-neti, the confusion is resolved.
The body appears IN this subjectivity, TO "I". The mind or thoughts appear IN this subjectivity, TO "I". A lifetime of experiences have appeared TO this "I". Yet this "I" has never appeared. You cannot describe "I". You cannot measure "I". You cannot conceptualize or split up "I".
All objects come and go in your Presence - the Presence of "I". And this "I" is like a mirror - the basis or ground for all experience - like a mirror required for the reflection to appear. The reflection is MADE OF mirror. The world is MADE OF "I".