Six in the third place is the hexagram's instruction to stop. A querent drawing it is being told that coming and going lead to the same defile, that effort at this point deepens the situation rather than easing it, and that no action at all is the correct course. This is rarely what somebody in difficulty wants to hear, and the line is worded so that the counsel cannot be mistaken for a recommendation to try something different instead.
The structure explains the severity. The stroke is yielding in an odd place, incorrect by the standard rule, and it stands at the join between the two Kan trigrams with water below it and water above. The second line could gain a little because it was strong and central; this line is neither, and it has moved past the point where the lower trigram offered any footing without yet reaching anything the upper trigram provides. Every direction it can face opens on more of the same.
The changing line turns the lower trigram Kan into Xun and produces The Well, King Wen 48, a source that does not move and is not diminished by being drawn on. Read against a line forbidden to act, that is an unexpectedly generous destination. What replaces movement in a time of doubled danger is a fixed point other people can come to, and the stillness this line demands is what makes such a thing possible at all.