Great Power opens with strength in the wrong place. Legge's translation shows the subject manifesting his vigour in his toes and states that to advance on that footing brings evil, with certainty, while the commentary on the image says it will lead to exhaustion. The hexagram is thunder above heaven, four strong lines rising under two yielding ones, and after the doubled Qian it is the most vigorous figure in the classic. This line is that vigour before it has anywhere to go.
The toes are the lowest part of the body, and the first place of a hexagram is where nothing has yet been built. A strong stroke correctly placed in an odd seat at the base of the lower trigram Qian is genuinely powerful and genuinely without position, and the combination is what the text objects to. Power at the bottom is measured not against an opponent but against the distance it would have to travel, and the certainty in the verdict is worth noting, because the classic rarely says that evil is certain.
The Great Symbolism draws from thunder rolling above heaven the counsel that the superior man takes no step which is not according to propriety, and this line is the first test of it. Nothing is wrong with the strength itself. What is wrong is that it has been shown at the toes, where showing is the only thing it can do. The exhaustion the commentary predicts is the price of a movement made on capacity alone with no standing behind it.