Many or most people achieve Final Participation quite frequently - and in a reductionistic, psychological sense it isn't all that difficult to do so.
The problem is that achieved Final Participation is not noticed; or when noticed it is rejected as unimportant.
In a minimal sense - Final Participation is happening to me in those, mostly brief, 'moments' when I look at the stars or a beautiful and beloved landscape, read and really 'get' The Lord of the Rings, am suddenly moved by music and recognise it happening to me, or become aware of myself among my family, or awaken in the night feeling my-self to be at the centre of a great field of awareness.
That is IT - but it is generally regarded as trivial or delusional - just a random firing of neurons, or evidence of the human ability to imagine themselves more significant than they really are... In a word: the subjective experience is regarded as merely subjective - and having no relevance or importance to anybody else or any-thing else.
And this interpretation is understandable; because by this-worldly criteria it is nearly-always true.
For a start - we expect to be overwhelmed by reality (when it is really-real). We figure that anything real will impose-itself on us, so that we cannot resist it - that we will be swept-along by real-reality... so brief and delicate moments are not what we are looking for.
But being overwhelmed would not be a good thing; not for an adult; not for a soul that is aimed at becoming fully a part of the divine family...
If we are ultimately to become fully divine, and to participate in God's works of creation - then (to be valuable, for each to make a substantive contribution) we must be operating from a situation of full agency.
This, in turn, means that we need to to be consciously aware of our own thoughts, and of the ultimate realities external to our-selves. We cannot be immersed unconsciously in reality, we ought not to be overwhelmed nor swept away by reality. In contrast, we need to be able to stand-outside of reality and perceive reality and our-selves, and the creative integration of original thought from our-self and the already-existing reality.
And secondly - our interest in reality is typically a (covert) interest in power. We are prepared to believe that something brief, delicate and subjective is real if - like mathematics, science, and engineering - it promises to bring us power.
Such power might be personal enhancements (such as money, a job, high status) or it might be more remote and idealistic power - the power to build a bridge or cure pneumonia... but our interest in subtle, non-overwhelming reality is linked to our optimism that it will have 'cash-value' in our mortal lives.
(To put it another way: Almost all people, almost all of the time - are doing things for reasons of 'power' (by this broad definition); and, for obvious reasons, none of these people can be allowed anywhere near teh process of creation - or else creation would be poisoned and destroyed. But the prevention it does not really work by exclusion; it works by inability... Anyone motivated by person power - 'egotism', pride etc. - thereby automatically and totally excludes himself from participating in the creative process.)
So we seldom notice Final Participation because it is outside of our metaphysical assumptions about what is really real - but even when we do notice it, our interest usually fades rapidly when it becomes apparent that we cannot (under any circumstances) use that knowledge to get power to improve our mortal lives: when we realise that such knowledge is not power.
Indeed, the knowledge that we get from such moments as I listed is not easy to share - it is not translatable into the common language of our times - partly because that common language excludes such matters, and partly because we don't even know how we might be able to communicate or explain such matters beyond (as I did above) merely describing the situation in which it happened.
It seems that an important part of it is that there must be a direct form of knowing, a knowing without communication - so that two people might know exactly the same thing without sensory perception or having to interpret symbols... by some mechanism whereby the same knowledge is being (simultaneously) shared...
Since the entirety of modern culture is based on the assumption that no such mechanism can exist, that all knowledge arises by a complex, multistage and unreliable chain of communication-steps... well we can barely even formulate the possibility of direct knowing.
However, however, however... If we are able to understand that these brief and delicate moments of Final Participation are In Fact direct glimpses of truth and reality; attained because our minds are (briefly) attuned with the divine creation - we can see why they are brief and incommunicable; and we can also see why the knowledge we attain is disconnected from power.
When we are directly observing divine creation, we are indeed only one step away from actually joining-in-with divine creation - but that is a vast step, seldom taken. It is one things to observe reality - but another and qualitatively more-difficult thing to engage in the making of reality; because for creation to continue entails that it be coherent, harmonious - that all additions to creation be fruitful and (of course) Good.
You and I are (almost certainly) a very long way from being able to contribute to divine creation; because we are not in harmony with the divine. (In other language, we are creatures of sin.) But I am not saying it is impossible for a mortal Man to add something to creation - indeed, that is precisely what a true creative genius has done (done objectively; whether or not recognised by fellow men).
But we can also see that the situation in which this happens is rare and unstable. When the situation is right, when a person is (however briefly) truly aligned-with the goals of divine creation - when he observes and loves creation... then it may be that his own divinity, his own agency, may not only observe but also contribute to on-going creation in some way - quantitatively microscopic, but eternal and therefore significant.
Perhaps, indeed, there is do distinction between observing and co-creating; perhaps these ephemeral moments of Joy are in fact our own, individual, nano-contributions to the actuality of divine creation? I would not rule it out - and indeed perhaps this is why we are mortally alive - our destined purpose. Perhaps the contributions of mortal men - no matter how small and infrequent - offer something of great and permanent value to the vast totality of God's creation?
Yet even if or when this happens, there need not be any observable relationship with mortal life in this world. Such a happening is Not about power, Not about 'will power', not about the limited situation of a 'successful' (comfortable, convenient, pleasurable) mortal and earth-bound life; but way beyond and above and far wider-than such superficial and ephemeral considerations.