We all need an element of mystery in our lives, whether it is through books, music or art. Mystery is a space in which we can lose ourselves and conjure up our own personal thoughts and feelings. It is a place-holder, a space that no one can dictate to us what we should be thinking or feeling. It is ours to own.
I remember reading an article by the late Galen Rowell (he died in 2001 before the digital revolution really took off) describing a day when we would have so much control over our images that we may be too obsessed by having detail right down in to the deepest of tones in our work. His concern, if I remember rightly, was that many images would lose any sense of mystery. As he pointed out in his article, humans have always seen mystery in darkness or areas of the landscape were it is impossible to define shape or detail. Our primal instincts tell us that dark places can be full of unknown dangers and that we must be careful. I think that when we look at images where there are lots of dark tones, with almost no definition, we tap into that primal instinct.
I really love playing around with the full tonal register available to me. Sometimes my images are deliberately very bright while other times the images are consciously very very dark. It's something I feel I'm still learning to flex my visual muscle with, but at the back of it, is Galen Rowell's article from 2000 reminding me that shadows convey mystery.