We all think we know everything. Not in an intellectual sense, but in the sense that we think we have a good grasp of reality based on our limited experience. We think we know and understand life and reality based on what we have experienced. Didn't Aristotle say, Nothing exists in the mind that was not first in the senses?
In a sense, we are the sum of our experiences, so it makes sense that it is difficult to imagine a life beyond this one or even experiences beyond our own.
I'm not attempting to limit our imagination here. My only point is that we operate on the fact that our experiences have given us an accurate portrait of reality; but how could that be an accurate portrait if there is so much we haven't experienced?
This is even illustrated by modern phrases: "Getting perspective," "Seeing the big picture", "Not seeing the forest for the trees."
I was just thinking about how limited our view of life, and reality, and eternity is, and how easy it is to put so much focus and emphasis on this one little point in time when our life is but:
...a vapour, that appeareth for a little time, and then vanisheth away.
-James, in his letter to the scattered Christians
If I seem to be waxing a bit too philosophical, blame it on Thomas a Kempis (The Imitation of Christ) and C.S. Lewis (The Screwtape Letters).