There were so many books on the shelves of my uni library that were based on the derivative of "Beauty is truth, truth is beauty" etc. About three metres of shelving worth. It was an Art library, so it had all the things - poetry, theory books, rambling philosophical prose on Art, and so on.
But that derivative quote of Keats is definitely one that sticks with me, so it made me pay more attention to your post :)
As a photographer in my other life (I have too many lives) the shape of darkness is a place I can add mystery or hide things, or, if I'm being really skilled, suggest at the presence of something else - and if I'm being the most skilled I possibly can be, in that darkness tell the viewer exactly what they're going to see, and feel, based on what isn't in the light.
There is always something in the shadow - and that's entirely a good thing - that is where we can find hidden detail, meaning, feeling, and messages that are not always apparent. If we investigate both the shadows and the light, then and only then, can we have the full picture, because without the stuff in the light, we would never get the shadow.
RE: What Shape Does the Darkness Have? (Ode to a Grecian Urn)