To all... a momentous new year...!!
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(I pretty much just copy pasted lol. But I first learned about this is a Manhua (chinese manga). I'm by no means knowledgeable on the subject so if you want to really learn about it I'd suggest doing some of your own research :P )
The trigrams are related to the five elements of wu xing, used by feng shui practitioners and in Traditional Chinese Medicine. Those five elements are wood, fire, earth, metal, and water. The Water (Kan) and Fire (Li) trigrams correspond directly with the Water and Fire elements. The element of Earth corresponds with both the trigrams of Earth (Kun) and Mountain (Gen). The element of Wood corresponds with the trigrams of Wind (Xun) (as a gentle but inexorable force that can erode and penetrate stone) and Thunder (Zhen). The element of Metal corresponds with the trigrams of Heaven (Qian) and Lake (Dui).
☰ | 乾qián | the Creative, Force | heaven, sky天 | northwest | father | head | strong | creative | 馬 horse
☱ | 兌 duì | the Joyous, Open | pond 澤 | west | third daughter | mouth | pleasure | tranquil (complete devotion) | 羊sheep, goat
☲ | 離 lí | the Clinging, Radiance | fire 火 | south | second daughter | eye | light-giving, dependence | clinging, clarity, adaptable | 雉pheasant
☳ | 震zhèn | the Arousing, Shake | thunder 雷 | east | first son | foot | inciting movement | initiative | 龍dragon
☴ | 巽xùn | the Gentle, Ground | wind 風 | southeast | first daughter | thigh | penetrating | gentle entrance | 雞fowl
☵ | 坎kǎn | the Abysmal, Gorge | water 水 | north | second son | ear | dangerous | in-motion | 豕pig
☶ | 艮gèn | Keeping Still, Bound | mountain 山 | northeast | third son | hand | resting, stand-still | completion | 狗wolf, dog
☷ | 坤kūn | the Receptive, Field | earth 地 | southwest | mother | belly | devoted, yielding | receptive | 牛cow