My take on the fourth :
As three dimensional people, our vision is limited to seeing everything in sort of special two dimensional view. We can never physically see all six faces of a cube at once, but we can understand that there is depth. Without depth, people would unfortunately see everything as directly in front of them. Even the farthest object seem to be the same distance away from everything else. Some people do see like this, suffering from a depth perception disorder. This depth perception defines our ability to understand the third dimension.**How, then, do two objects in the fourth dimension see each other? It is my belief that beings in the fourth dimension see each other as true three dimensional objects, with a sort of "depth perception" that acknowledges the presence of the fourth dimension. That is to say, they can see all six faces of a cube at once, as well as being aware of the fact that there is a sort of "depth" to what they see. They are incapable of seeing all eight faces of a 4D cube, but can clearly see most of the multiple 3D cubes that makes up the faces of the 4D cube.
Let's go back a step. Imagne you're a 2D stick figure. The most complex thing you can understand fully is a square, but even the you will never be able to see all of a square at once. In fact, since you will only see two faces of the square at most, all you could ver see is a single line from your perspective. That is, a 1D figure. But, at the same time, you know that there is more to that line because of you're ability to perceive two dimensional (2D) depth.
This is, at the very least, how I understand why is it I cannot truly perceive what a 4D cube would look like. Any thoughts?