The thirty-ninth hexagram, Jian ("Obstruction" or Difficulty), places Kan (Water) above Gen (Mountain). Danger, the abyss, lies ahead while the mountain stands behind, the image of an impasse with peril before and a barrier at ones back. It follows Opposition in the King Wen sequence.
Jian stands 54th of 64 in the xiantian, or Earlier Heaven, arrangement, the binary ordering devised by Shao Yong in the eleventh century and ascribed to Fu Xi, distinct from its thirty-ninth place in the King Wen sequence traced above. This was the arrangement Joachim Bouvet, a Jesuit in Beijing, sent to Gottfried Wilhelm Leibniz in 1701, letting Leibniz read its broken and unbroken lines as his own binary 0 and 1.
Read from the bottom, the six lines of Obstruction run yin, yin, yang, yin, yang, yin. A later interpretive layer absent from the original Zhou Yi, the nuclear hexagram (hu gua), treats lines two through four as a lower trigram and lines three through five as an upper one; here they combine as Li over Kan, forming hexagram 64, Before Completion (Wei Ji), a hidden figure first associated with the Han-dynasty scholar Jing Fang, whose Yijing commentary of the first century BCE is credited with the earliest appearance of nuclear trigrams. Obstruction's King Wen partner is hexagram 40, Deliverance (Xie); most of the sixty-four pair this way, related by turning the whole figure upside down, while the eight hexagrams built from a single doubled trigram pair instead by inverting every line. Mawangdui (1973) orders hexagrams by trigram, not King Wen; names here follow Wilhelm and Baynes, 1950, not Legge, 1882.