Existential Reality is the source of true Truth, everything else is an attempt that shall fail inevitably, we only wish for them to linger long enough to facilitate a new generation of tries.
Trusted institutions and establishments are for whoever they serve. Identity and the stories we tell ourselves are closely related. Institutions and establishments provide a narrative. Everyone wants to believe their narrative is correct and meaningful, even when it is contradicted by those of others.
The answer to your riddle is that no one is a definitive source of "truth". A story of "truth" is a form of technology. The more consistently useful representation tends to prevail (of which astrological charts are as accurate as scientific predictions of human behavior.)
Notice that "more consistently useful" does not mean "true truth". Won't you invest in narratives that get you paid, or laid, or accepted?
True truth requires a cult like fastidious intention toward integrity (consistency) with existential Truths (observable, imperical, reproducible). Such austerity is not necessarily advantageous socially, economically, or politically.