My point is that we could live all our lives completely oblivious of something that is a vital part of our life. This brings out the questionable nature of what we call knowledge...and our natural abilities and limitations to actually know the world around us.
I think it is fairly uncontroversial that humans are oblivious to a great deal. Whether this is an issue that should necessarily concern us is a very different matter. Like other animals we evolved a variety of sensory abilities that helped us to survive, and we use data from these senses to model the appearance of a world which, for all practical purposes, we take to be 'the world'. Other creatures will model their worlds according to their own faculties. Such
Umwelten overlap but will not necessarily be contiguous. It doesn't follow from this that any particular organism suffers from a deficiency of some vital knowledge of the world. We manage quite well without sophisticated echolocation, for example, or the ability to see and hear at wavelengths and frequencies available to other animals. The point is that all creatures are necessarily limited and this isn't in itself obviously a problem. How could it be otherwise?
The suspicion that the universe is harbouring some kind of vital secret that it discloses only to a select few seems to be a peculiarly religious preoccupation. With what faculty exactly do these chosen ones discern this hidden knowledge and how is it that they alone possess this facility? More to the point, why do they so manifestly not agree on what it is that they perceive with their special senses? In light of this, how should the rest of us view the strange and varied claims of those who purport to have access to a vital but intangible dimension of experience? Clearly we cannot believe all of them so on what grounds might we judge which should be taken seriously and which dismissed? We cannot even rely on the claim that a particular spiritual method will yield similar knowledge. The historical Buddha, for example, trained in meditative methods that took the existence of a True Self for granted and yet it led him to refute the same. Do we believe him or his teachers?
But it seems to me that there is something more fundamental here that should enlist our caution. Is it not a bizarrely paranoid neurosis to worry 'that we could live all our lives completely oblivious of something that is a vital part of our life'? There must be a potentially infinite number of allegedly vital things we don't know, yet strangely we carry on without them and not obviously any the poorer for it. How might we even judge whether a given claim of vital knowledge is indeed vital? Would it be vital for everyone or just those who seem unable to cope without it? Might it not be more pertinent to ask why some people seem to need such beliefs while others manage perfectly well without them? Which of these two groups is deficient? The belief that there is vital secret knowledge to be sought is surely itself a sign of something psychologically lacking. Why is it that for some the (everyday) world is not enough? I think Thoreau once wrote that a person is rich in proportion to the number of things they can do without. Maybe the greatest wealth lies in being content with our limited earthly life. After many years of meditation the first Zen patriarch is said to have announced, 'In truth there is nothing to find.' Perhaps that is the secret we need to discover.