It is only our dualistic thinking that makes us think that we are not. Our little mind always wants to find a conclusion, to reach a finishing line. It cannot fathom infinity or eternity. The little mind thinks in terms of beginnings and endings. To fathom infinity, you cannot use the mind.
Mind is ungraspable, empty.
When we look, we see that this very Mind is no mind. It has no boundary, no outside, no limit. It will cost you your life. And if you have a picture of what it is supposed to look like, that is just an obstacle. Having an opening is seeing it.