The topmost line is a punitive expedition kept at home. Legge's translation shows the subject advancing his horns and using them only to punish the rebellious people of his own city, calls the position perilous while granting good fortune and freedom from error, and adds that even under firm correctness there is occasion for regret. The commentary on the image concludes that the course of procedure is not yet brilliant.
Punishing a rebellious town was an ordinary instrument of government in the period the text comes from, and the line is written from inside that practice rather than around it. It is given here as the text gives it. What the line does with the practice is what survives the change of setting, and it is a restriction: the horns go out and are then turned back on the subject's own domain. Force at the summit of Progress is licensed only against what the person is already responsible for.
The stroke is strong at the top of the trigram Li, past the yielding ruling line below it, and the sixth place is the classic's station of excess. Horns are what an animal has when it has run out of other arguments. Everything this hexagram has achieved by brightness, by being seen and being trusted, is at this station being pressed by force instead, and the qualified verdict, good fortune with regret still attached, is the text declining to call that an advance.