Folly is an inseparable aspect of humanity. It is essentially linked to self interest. Every generation, many people fall victim to frauds - that is, to other's self interest - in the pursuit of their own.
The idea that there is something new under the sun appears to be mostly linked to the ignorance of youth. Hopefully people learn while there is less to lose.
The modern world, in general, believes religion constitutes a vast fraud. There are, of course, innumerable instances of individuals perpetuating fraud via religion to support this conclusion.
Yet religion persists, in one way or another. In general, the world still has faith in science and its products. There are, of course, specific instances to support this idea, but the faith is a broad acceptance.
We all, especially in our moments of weakness, desire parental assistance. That is, a believable source of truth and something we can believe in - our own intellect, of course, limited. So at one time this was dominated by God, but now it is dominated by systems and bureaucracy. That is, the government, the medical industry, the media complex, etc.
Traditionally, religions emphasize obedience in the face of this Human Folly. This is a parental quality: you may not understand why running in the street is dangerous, and until you are old enough, you must obey.
Of course, we always think we're old enough sooner than we are.
So how does one know? That is, in the face of massive deceit, ignorance, self delusion, and perpetual human error - how is one to know?
I think Bruce Charlton has elaborated a foundation, and it is the core of Christianity. We must recognize the above situation, but still try our best. This life, as a whole, is situated as to provide us with the possibility of spiritual progress. We must, indeed, try our best - and to always be ready to repent our errors.
That is, it really is about personal choice. Especially perhaps in our particularly modern circumstances. Where many of us don't have the option of simple obedience - or even where those whom we should simply obey appear to have lost their way - we must make the active and personal choice to believe in God instead of meaningless. We much take each step, though difficult, and expect personal error and folly.