At the summit the hexagram turns on itself. Legge's translation shows the subject exciting himself to long continuance and gives evil, while the commentary adds that far will he be from achieving merit. Every line below has been about steadiness of one kind or another, and the figure closes with somebody working hard at being steady, which the text treats as a contradiction rather than as an excess of a good thing.
The distinction is between a state and a performance of it. Duration in this classic is a course renewed quietly inside a fixed form, and the Image counsels the superior person to stand firm and not to change their method. Agitation directed at that end destroys the end, because calm was what had been asked for and effort spent producing calm is not calm. A person visibly straining to be constant has already stopped being constant.
The stroke is yielding in an even seat, correct by the ordinary rule, at the top of the upper trigram Zhen. Zhen is thunder, whose attribute is arousing movement, and a line at the extremity of that trigram is movement at its furthest reach. In a figure that pairs thunder with wind precisely so that motion and penetration temper one another, the topmost line is where the motion has run past its partner and is shaking on its own.