The chapter states the book's central claim about softness and then adds a sentence that complicates every other chapter in it.
Nothing in the world is softer or weaker than water, and yet for attacking what is hard and strong nothing can surpass it, and nothing can take its place. That the weak overcomes the strong and the soft overcomes the hard is known to everyone in the world and practised by nobody.
The admission is remarkable. This is the doctrine the text argues for from chapter eight to chapter seventy-six, and here it is described as common knowledge. The difficulty is relocated entirely from understanding to practice, which is the same diagnosis chapter seventy gives when it says the words are easy and nobody can act on them.
Two consequences follow for how the book reads itself. It is not claiming originality, and it never does anywhere else, preferring to attribute its positions to the ancients and to what was formerly said. And it does not think argument is what is missing, which explains why so much of the text is imagery and repetition rather than demonstration.
What is missing, on the chapter's own account, is the capacity to act on something you already believe when the situation offers you the other option. Water wears through stone over a timescale nobody has, and the person who knows the principle still reaches for force because force works this afternoon.