If you can only see an infinitely small part of a line, it looks like a dot, one dimension is reduced to zero dimensions. You are not aware of the true nature of the line.
If you can only see the smallest part of a two dimensional plane, it looks like a one dimensional line, apparently. Furthermore the smallest part of a three dimensional volume is a plane, and in observing the plane, you are unaware of the whole concept of volume.
Therefore the only part of the four dimensional Hyper Universe we can see is the bit the protrudes into our consciousness, and that is the three dimensional universe we know and love.
Here is part of our observable Universe.
There's obviously a lot more involved with the Hyper Universe.