The fourth line of The Well (King Wen 48) is drawn as yin, the numeral six in the old divination manuals. James Legge's translation renders the line as the well lined with brick, no error. The image sits inside a hexagram whose judgment as a whole concerns a town may be changed while the fashion of its wells is never changed, the well neither decreasing nor increasing, and all who come and go draw from it and are benefited, 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 Kan, water in Legge's readings of the eight trigrams, while the lower trigram of the hexagram is Xun, wind in the same traditional set of images. The Great Symbolism of the hexagram reads water above wood; the superior man comforts the people and stimulates them to help one another, and the fourth line takes its place inside that combined picture of Xun below and Kan above.
Read on its own the line neither opens nor closes the hexagram's argument. It marks the point where Kan is either forming (in the lower trigram) or completing itself (in the upper), and later interpreters treat its image, The Well Lined with Brick, as the concrete case through which the hexagram's abstract judgment becomes visible in a single situation rather than a general principle.