Nine at the top gives a querent permission to use force and then immediately fences the permission in. The horns are advanced, they are used only against the rebellious part of the person's own city, and the outcome is dangerous, fortunate and free of error, with regret still attached even under firm correctness. Four qualifications sit on one act, and the accumulation of them is the counsel.
The practice behind the image is the period's own, a ruler disciplining a town inside his own territory, and it is reported as the text reports it. Read for the structure rather than the setting, the line draws a boundary that transfers cleanly to any situation: at the end of a successful advance, force may be applied to what one already governs and to nothing beyond it. The commentary withholds all praise, noting only that the procedure is not yet brilliant, which stops the permission reading as approval.
When the line changes, the upper trigram Li becomes Zhen and the figure becomes Enthusiasm, King Wen 16, thunder coming out of the earth and a movement that other people join willingly. That destination is the alternative this line has not taken. What is being achieved by discipline at the top of Progress could have been achieved by a movement people wanted to be part of, and the regret the text leaves attached is the distance between the two.