Owning Your Own Shadow by Robert A. Johnson
A requirement for fully developing your own mind is coming to terms with your own inner Shadow. That part of your Psyche which produces unwanted thoughts, habits, and actions. The author describes what the Shadow is in a way that is easily understandable. In my own experience examining my own life, his ideas and theories make very logical sense. When I have a framework to categorize my own mind, it's not hard to see where I have unexpressed aspects of my own Self that deserve my attention. At a mere 118 pages of above averaged sized font, this book is a very efficient way to begin building a framework which I've found to be accurate and helpful.
According to his theory, every time a person fails to express their inner desire they feed or enlarge their Shadow which resides inside the psyche and is the cause of that behaviour which we all have, but wish we didn't. That habit you know you shouldn't feed, but just can't work up the energy to stop. That crutch you keep falling back too whenever the stress of life throws you off balance. Those hateful words you shout at someone you love which you later regret. These are all examples of how the shadow can influence the day to day life of people. With the right knowledge the shadow can be balanced through one's action and thought to the point where they become Light and no longer negatively impact the person. This knowledge is primarily Knowledge of the Self.
This book was based off of his working experience both with patients and his own experience practising deep Inner Work which is commonly called Active Imagination in the jargon of Psychology. As someone who has studied and practised this form of meditation alongside more esoteric subjects derived from the Mystery Traditions, I can say they are both tapping into the same inner currents. The AI technique was created by Carl Jung, who also happened to be the founder of the current scientific theory of the psyche which is practised as Jungian Psychology nowadays. AI was my own personal stepping stone into the Mystery Traditions and if I weren't drawn to the traditions of my own ancestral roots I would surely still practice this non-secular form of Inner Work.