As a divinatory line, nine at the fourth place of The Cauldron reads within the hexagram's overall concern with great progress and success. The line occupies a place that does not match its own nature in the classical doctrine that odd places favour a firm, yang line and even places favour a yielding, yin line. Its own text, that the caldron's legs broken, so that the ruler's food is overturned and spilled, its form drenched, an evil case, is the particular fortune assigned to this one stage of the situation, not to the hexagram as a whole.
The fourth line corresponds by classical convention with the first line, and the two correspond here, since one line is yin and the other yang. Read together with the trigram it belongs to, Li in the upper position of the figure, the line marks the first word of the upper trigram, close enough to the ruling fifth line to be shaped by it, one stage in the six stage movement the hexagram traces from its first line to its last.
A change at this line, from yang to its opposite, is the mechanism the tradition uses to move from one hexagram to another. Flipping the fourth line of The Cauldron turns Li into Gen while the other trigram, Xun, stays as it is, which yields The Cauldron's changing partner, Work on the Decayed (King Wen 18), the hexagram this line is recorded as transforming into.