To the Ninja, the Mind is the ultimate weapon. Development of the Mind can be achieved only when the body has been disciplined. To accomplish this, the ancients have taught us to imitate the Five Elements and the Eight Mystic Trigrams. From these come the physical exercises and techniques we practice in Black Dragon School. Thus, the Art is crafted and the body is trained.
To develop the mental skills necessary to fully utilize the special powers and abilities conferred by these methods, the Ninja practice codes and ciphers, much like the Cryptoquote given elsewhere on this site, and which can be employed in their trade of espionage, as well as crossword puzzles, riddles, mathematical games, and for the more philosophical principles, Koans. All designed to exercise the Mind and teach the student to think.
This grants the Ninja access to the incredible world of possibilities. Thus, when confronted with danger or need, the Ninja is not limited in his development of a solution. He is able to improvise, adapt, and overcome any obstacle, making him formidable indeed.
Some Koans take the form of questions, like the one that asks, "If a tree falls in the forest and no one is around to hear, does it make a sound?" There is no "right" answer to this question. It can be argued for years from either perspective, yes or no. BUT, to the Ninja there is at least one other answer. It matters not at all whether the tree makes a sound or not. What is important is that it has fallen.
Further, not all Koans come from Japan. One example is the famous psychological test: "Is the glass half full or half empty?" The Ninja is not limited to these two choices, because he is aware of this ploy to see if he is optimistic (half full) or pessimistic (half empty). Therefore, the Ninja uses an option that seldom occurs to other people: The glass is too large for the amount of water contained therein. Thus, it is neither half full nor half empty. And, there are many other "answers" equally as correct. The "trick" is to imagine them and exercise the mind. That is what makes them fun, and useful.
Learn not only to "read between the lines" but also "within the words" of each of these examples. There is always more than meets the eye.