As a divinatory line, nine at the fourth place of The Joyous reads within the hexagram's overall concern with progress and attainment, but advantage lies in being firm and correct. 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 deliberating over where to seek his pleasure and finding no rest, bordering on what would injure him, yet there is cause for joy in the end, 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 do not correspond here, since both lines share the same character. Read together with the trigram it belongs to, Dui 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 Joyous turns Dui into Kan while the other trigram, Dui, stays as it is, which yields The Joyous's changing partner, Limitation (King Wen 60), the hexagram this line is recorded as transforming into.