Since the advent of 'modernity; people have been - quite reasonably - concerned about the possibilities of subjective self-deception.
But this has typically been dealt with by the false idea of 'seeking external evaluation'; without any recognition that all external systems, models, sources and methods of external evaluation are prone to exactly the same problem of self-deception - but hidden by layers of incomprehensibility and complexity; and therefore ignorable.
I first confronted this in science; which has been widely regarded (in The West) for the past several centuries as the best and most reliable source of knowledge - exactly because it claims to have an objective method and external systems of evaluation.
Yet, when we look at 'science' as it has become over the past several decades (most evident since early 2020) - we ought to be able to perceive that this is nonsense; because 'science' is neither valid (ie true) nor even reliable (ie stable) - but instead fails to satisfy even common-sense efficacy, and spins like a weathervane to track socio-political imperatives.
This is evident from the inside of science, where I dwelt for much of my professional life; and where we can perceive the endemic and near-total prevalence of dishonesty. And that this corruption of science stems not from defective 'methods' (which have indeed been 'improved'... at least according to the lights of mainstream science methodologists) but from defective motivation.
When one has observed the indifference of scientists to truth - and especially among the most famous, successful, powerful and prestigious scientists; one can infer that the successful era of real science was never about method; but instead was about motivation.
It was the motivation to seek and speak truth that drove science, and made its validity and reliability.
Once that motivation was subtracted, then science became corrupt - and the expansion of 'methodology', the systems of 'external validation' (such as the evil nonsense of 'peer review') merely concealed- and distracted-from this corruption.
The same applies in the realm of the spirit.
It turns-out (as we can see from a glance at the gross dereliction of All the major Christian churches, most evident in 2020) - the vast apparatus of authorities, scriptural scholarship, and methods; has been utterly ineffectual in preventing wholesale corruption and co-opting of the churches to the agendas of globalist totalitarian evil.
It turns-out that external validation only reinforces error; and thereby prevents repentance.
If not, then what? If not external and group-orientated validation, then what?
Well, the answer is internal and personal validation: individual discernment.
But what prevents personal discernment from becoming merely an exercise in wish fulfilment, incompetence, delusion or self-deception?
The answer is - for Christianity just as for real-science - motivation.
If one is motivated to seek and speak truth about God, creation and Jesus Christ; then over the long term, one will naturally repent and discard error - whenever and in whatever form error emerges.
There is no method but motivation, no authority but motivation.
Someone who is not genuinely motivated to know God, will not know God - and will find a million ways of covering and denying his errors.
But someone who is motivated to know God has a million ways of discovering when he has erred; and of discovering true authorities (if any), true scripture, true methods - and truth in a million other places.
And when he makes a discovery of his own error, there is nothing to stop him repenting; because he will not wait upon the say-so of external authorities/ scripture/ methods etc.
When science was real, errors made little difference, because in a community of the honest - errors of truth were naturally detected and willingly discarded. But now that we have a system and method of fake-science, and science is defined as membership of this community - truth is of zero concern; and errors are adopted and maintained whenever, and for as long as, they are expedient.
The analogy of science with Christianity and the churches is exact.
The answer in both science and Christianity is for truth-motivated individuals to seek for themselves; confident that in a reality created by God our loving Father; he will always, in the end, be able to discover as much truth as he needs for the purposes of this mortal life.