He explained this point from the distribution of the five elements in the eight characters. The prosperity of the five elements shows that a five element is stronger in the eight characters. In most cases, these five elements may become taboo. Since it is taboo, she needs other five elements to restrain him, or she can promote other five elements to dissolve his powerful energy.
For example, in his five elements, the wood spirit is vigorous, and this wood spirit will restrain the soil in the eight characters, so at this time, there must be gold to restrain it, or fire to vent his wood spirit, so that the wood spirit can become peaceful. That's what he meant.