Accept that your senses - all the biological organs you are using to receive input from the external "authorised" reality - are flawed.
Let us be generous and say that your own personal projection of the external is about 95.7% accurate. The fact that you continue to read this speaks volumes of your own cerebral capacities so yours is probably 0.5 or 0.6 percent higher. Our concerns are with the broader populace and so we must disregard our own obvious superiorities and consider 95.7% the accuarcy rating of our human perceptions.
Only 95.7% of what you observe, hear, feel, taste or smell has been processed accurately by the inadequate squishy grey/white jelly fluidicly suspended within your skull.

What of the 4.3% of incorrectly processed or imperceivable data?

Much of it is pseudo-random nonsense of little use to anybeing. The perceptual parallel to atmospheric noise. Billions of nuggets of nearly-nothing sifted and rejected by the minds filtration mechanism and left to roam between the spheres of awareness of concious minds.

What remains beyond that?
Well, that would be us.
OOC - The agony of understanding.