For example, consider this statement in the Daodejing:
“In order to contract, it is necessary first to expand. In order to weaken, it is necessary first to strengthen. In order to destroy, it is necessary first to promote…”
One part of the pair comes after the other, back-and-forth reversal, as in a cycle.
The meaning of one term becomes clearer by knowing its opposite. For instance, if we know hot, then we understand the meaning of cold better.