That's a common greeting in my part of the world. "Not too much!" comes the good-natured reply -- or we may just give a slightly startled laugh. After all, if taken seriously, the question can be rather unsettling.
We may have wondered just how much the human mind can know for sure. So many of the "facts" of this world that we take for granted rest on shaky foundations. But we can be more certain of what's true, eternally true, as we get better acquainted with God. What He knows is for sure, because He is the only true creator, the one infinite Mind. His image, man, is forever conscious of the truth He knows and has established. Our knowing, then, more nearly approximates the divine as we realize that God alone is Mind, the source of eternal truth.
For example, the flu once threatened to overwhelm me during a six-hour car trip with several other people. I started to pray, but at first my prayers were more like wishes that the long trip would be over so that I could be by myself and sleep in my own bed for a while. When the distress was most acute, I found myself turning to the one Mind, silently asking, "What do I know for sure?"
As I took stock of my mental cupboard it seemed pathetically bare, but even so I was receptive to the truth that Mind was revealing. The thought came that there was one thing I could unequivocally state and realize: God is Love. In desperation I sought to feel Love's presence, which would quiet my shaken, quaking consciousness. I knew without a shadow of doubt that divine Love loved me and every other living creature. With awe, I felt the reality and radiance of that infinite Love, and I was healed. The rest of the drive was a pleasure, and there was no need to retire when we reached our destination.