As a divinatory line, nine at the first 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 proper to 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 pleasure of inward harmony, good fortune, since nothing in his conduct gives grounds for doubt, is the particular fortune assigned to this one stage of the situation, not to the hexagram as a whole.
The first line corresponds by classical convention with the fourth 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 lower position of the figure, the line marks the opening of the situation, before the trigram above it has any part in the reading, 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 first line of The Joyous turns Dui into Kan while the other trigram, Dui, stays as it is, which yields The Joyous's changing partner, Oppression (King Wen 47), the hexagram this line is recorded as transforming into.