Hexagram 12 is Heaven above and Earth below, which is the arrangement anyone would draw if asked to put heaven and earth in their proper places. It is also, in this book, the picture of things not working.
The reasoning is the same as for its partner, hexagram 11, and it is the clearest illustration of how the trigram commentary thinks. Heaven rises and Earth sinks, so with Heaven on top and Earth beneath, the two move apart. Nothing meets. Nothing is exchanged. Wilhelm's judgement has heaven and earth not uniting, the great departing and the small approaching, and the counsel that the superior person should fall back on inner worth and refuse honours and salary.
That last instruction is the hexagram's distinctive practical advice and it is unusually specific. The counsel is not to endure the bad period but to withdraw from public life during it, decline advancement, and avoid being conscripted into an arrangement that is failing. Legge's rendering keeps that sense; so do the later translations. It is one of the passages where the text is clearly addressed to an official rather than to a general reader, and it is a useful reminder of who the book was compiled for.
The name Pi is variously translated as Standstill, Obstruction, Stagnation and Blockage. None is wrong; the word covers a stoppage of communication rather than of activity, and translations that suggest inactivity slightly miss it. Things are happening. They are simply not connecting to each other, and no amount of additional activity will make them.