that's true.
I believe what helpmeh is driving at is the conceptualization of a 4-dimensional hypercube, and a universe that supports this fourth dimension. One cannot fathom what such a universe would appear as to one of it's inhabitants, being restricted to this lowly 3-dimensional universe of ours.
One can take the same concept the other way, for example, "flatlanders" takes the concept of being living in a 2-dimensional space trying to comprehend a third dimension.