A major belief of Gestalt theory is that of something existing both as a whole and of its interacting parts that can be separated and analysed.

And Edgar Rubin’s discovery (1915) of figure-ground perception in Gestalt psychology, leads us to those puzzling images where some of us see one thing, some another, and some of us both or all the images in the picture.  The figure is the object you perceive; the ground is everything you see in the background, and according to Rubin, we tend to simplify every visual image we see by separating it into figure and ground.