Hexagram 7, The Army, sets Earth above Water: water gathered and hidden beneath the ground, the many contained within the one, an image the Judgment reads as a multitude organized under a single leader for a serious, even dangerous, common purpose. The first line stands at the very base of the lower trigram, Kan, before the campaign has properly begun at all, and its counsel is correspondingly foundational rather than tactical: an army must set out with strict discipline, since good order at the very start is what determines whether the whole undertaking ends well or in misfortune.
Nothing here concerns strategy, terrain, or the enemy; the line is entirely about the internal condition of the force itself before it is committed to anything. This matches the hexagram's own Image, which counsels the superior person to increase the masses through generosity, a statement about the foundation on which any collective effort rests rather than about the conduct of a campaign already underway. Read as the opening line of a hexagram built around organized, disciplined mass action, line one insists that the quality of that discipline is decided before the first step is taken, not corrected once the army is already moving.