There are always realms in this world that we can never enter. Just as beings in a two-dimensional world can never conceive of a Z-axis, and so can never reach the dimensions of a three-dimensional world, perhaps the same is true of us?
However, I believe that just because a realm is beyond our reach doesn't mean it doesn't exist. It's just that, as far as the world is concerned, their development tends more toward idealism, while we are materialists.
Perhaps they are actually right beside you and me. But for materialists like us, it is impossible to believe they exist. And if we don't believe in them at all, we will never see them…