In a two-dimensional world, an observer placed on the two-dimensional plane would not see two-dimensional but mono-dimensional figures.

That is, it would not see squares and circles but only the mono-dimensional projection of these, that is, it would only see straight lines.

For an observer to perceive two-dimensional figures, the point of view must be on a third dimension.

In the same way an observer who was in a three-dimensional plane would see the projection of three-dimensional figures or the projection of cubes and spheres like squares and circles.

In order to appreciate three-dimensional figures, the point of view must necessarily be in a fourth dimension.