What is the only thing you are absolutely certain of, the only thing you really know, that doesn't come through the senses?
What is the very basis for anything to appear?
The concept of "I" appears in thought. It appears as a conceptualization of the sensory input called "body" and "mind". The "I", no matter what you think it is, can only come as a conceptualization of something appearing.
To whom does the "I" appear?
You are the Ultimate "I" - the ultimate subject to all objects, even the object "body" or "mind". The real "I" is the very source of all that appears.
What is the only thing you know, that didn't come from the senses?
You know "I AM". Does that ever change? Does that ever move? Does that need anything? Can that ever lose anything? Does that ever suffer?
Can you deny "I AM"?
Do you need to evaluate or conceptualize sensory information to know that you are?
What is the only thing you know, that didn't come from and doesn't rely on the senses?
Take a look.