The focal plane is one. Think of it as an infintesimally thin sheet of glass that extends to the boundaries of your field of vision. It happens to be parallel to your sensor or film. Anything out side of that plane, technically, is out of focus. We try to compensate by stopping down, but this only masks the issue. As special as that unique plane is, there are other parallel planes as well, an infinite number of them. They are slices of reality much like the working of an MRI. Here, imagine these many panes of glass. Slices of life, from the back to the front. Are they separate stories, or different elements of one grander scheme? All the layers sandwiched we call our world...only the finest palettes can find delight in such an array of flavors.