I attended a talk where the speaker said something along the lines of the only thing I can be certain about is that I am here, and body breathes and have weight on the floor.
When I look into this for myself, I find that the only thing I can be certain about is that there is awareness and content of awareness. And that this content of awareness is awareness itself. It is its own content.
And I cannot be certain about anything within this content. Everything this content appears as are only appearances, filtered, interpreted and flavored in many ways. Any differentiation, and any characteristic, of anything within content comes from an overlay of stories, and an infinity of these stories are possible.
It may appear that there is an I here, with the rest of the world as an Other, but that comes from a story of a separate self as one particular region of what arises (a set within what arises), and the wider world as the rest. It may appear that body breathes, but that too comes from a story of a body, as a particular region of what arises, and a story of breath overlaid on particular sensations within this region. And it may appear that all of this happens within space and time, but space is a story overlaid on what arises, creating the appearance of space, and time is another story, creating the appearance of continuity.
All of this happens in immediate awareness, and, when attention goes there, is seen as it happens.