The I Ching or Yi Jing, usually translated as Book of Changes, is an ancient Chinese text used for divination. For this kind of divination, bundles of yarrow stalks are thrown on the ground. Depending on how they fall on the ground, they form one of the 64 hexagrams, which can be looked up in the I Ching. The explanations in the I Ching are, however, very open to explanation. In my opinion, you have to know something about Daoism to be able to understand them.
Some scholars claim that the shorter and longer lines of the hexagrams represent clouds and the sun. Others say that it might be a vessel whose content changes, so it may be linked to alchemy, which I personally find very interesting. In any case, the short, broken lines represent the yin, and the longer lines the yang.
If you want to try divination with the I Ching yourself, it is not easy. To this day, it’s not known exactly how the yarrow stalks are related to numbers or the hexagrams. Some people nowadays also throw coins, special dice, or use cards.
In “The Glint of the Luopan”, the I Ching is a strong guide in Lijie Fang’s life. When he’s young, his grandmother teaches him the ancient wisdom, and he encounters it again in the Academy of the Dreamer Society. He and his future wife, Tang Li, often throw the yarrow stalks for fun.
Oh, by the way, the I Ching has been used in fiction before, of course – among others in Philipp Pullman’s His Dark Materials, where it guides the physicist Mary Malone on her interactions with Dust/Dark Matter and leads her to another dimension.