The fourth line of Development (King Wen 53) is drawn as yin, the numeral six in the old divination manuals. James Legge's translation renders the line as the geese gradually advancing to the trees, perhaps finding a flat branch to light on, no error. The image sits inside a hexagram whose judgment as a whole concerns the marriage of a young lady, and the good fortune attending it, advantage in being firm and correct, and this line supplies one stage of that larger reading rather than a complete statement on its own.
Structurally the line stands at the lowest place of the upper trigram Xun, wind in Legge's readings of the eight trigrams, while the lower trigram of the hexagram is Gen, mountain in the same traditional set of images. The Great Symbolism of the hexagram reads a tree above a mountain; the superior man attains to virtue that endures and makes the ways of the people good, and the fourth line takes its place inside that combined picture of Gen below and Xun above.
Read on its own the line neither opens nor closes the hexagram's argument. It marks the point where Xun is either forming (in the lower trigram) or completing itself (in the upper), and later interpreters treat its image, The Geese Gradually Advancing to the Trees, as the concrete case through which the hexagram's abstract judgment becomes visible in a single situation rather than a general principle.