The symbol is actually a representation of completion. The two complementaries (being/substance/necessity and becoming/action/actual) exist within the whole (possibility/quality). That is why I prefer the Russian nesting dolls, or the Venn diagram, to represent the Trinity (is it the “Jew god”? see here) as mutual production of all three, or the necessary subsuming the possibilities subsuming the actual.
But the tao also works because the Holy Spirit is from both the father and the son.