The chapter contains the book's most usable single piece of advice and it is not paradoxical at all. Plan for the difficult while it is easy, and do the great while it is small, because the world's difficult things are certainly done while they are easy and its great things are certainly done while they are small.
Stated that way it is a claim about timing, and it is the practical counterpart of the doctrine of non-action. A problem addressed at its onset requires almost nothing, and the same problem addressed later requires force. The person who acts early appears to have done nothing, because there was nothing visible to do, which is why chapter seventeen says the people credit themselves and chapter twenty-seven says the good traveller leaves no tracks.
The chapter draws the conclusion explicitly: the sage never does anything great and is therefore able to accomplish greatness. That is not modesty. It is a description of what a life of early intervention looks like from outside, which is a life with no great deeds in it.
The opening lines are stranger and set the register. Act without acting, work at not working, taste the tasteless. Treat the small as great and the few as many, and repay bitterness with power.
That last clause is a moral instruction of a kind the book rarely gives, and it was noticed early. Repaying resentment with power, or with virtue, is a position on how to answer injury, and it was taken up and argued with in the later Chinese tradition, where the competing view held that injury should be answered with straightness and only kindness with kindness.