The town may be changed,
But the well cannot be changed.
It neither decreases nor increases.
They come and go and draw from the well.
If one gets down almost to the water
And the rope does not go all the way,
Or the jug breaks, it brings misfortune.
(Hexagram 48, I Ching ; Chinese text here)
I know, Wilhelm is far from perfect, but it is ready to hand and sensible enough. I linked to the Chinese just because I could. I can’t read a lick of it, but it was easy to add the link and easy enough for a reader to take a quick look.