What if All be Error?
(As in: what if I'm wrong?)
I try to consider that possibility, constantly. There've been a few years (several within recent memory) that that's pretty much been my constant thought.
My view of humans, consciousness, knowledge, and truth, is that we are (or have) a sense-making organ, our brains, which we use to process the inputs we receive of our environment, to construct models of it, and then interact, on the basis of those models, with our environment.
The rationalists claim that reason, and reason alone, is the source of all knowledge. I believe this to be a cardinal error. It's the worst possible form of the map-territory confusion, in which we're mistaking the sense-making organ (brain) for the Universe. Since the brain and mind are subsets of the Universe, they can, at best, be only very small approximations of it.
The empiricists believe that experience and perception are the source of all knowledge. This is ... perhaps closer to the truth, but still incomplete. Perception alone is also incomplete. We see only a minuscule amount of all that happens, can focus intently (attend to, attention) only a tiny part of that. Our perceptions themselves are limited to a small range of stimuli: a small fraction of the electromagnetic specturum, a fairly accurate, though limited, range of sound frequencies. A grab-bag of chemical sensing capabilities via smell and taste. A range of heat, pressure, and vibrational sensations through touch, and a host of internal feedbacks to things which ... aren't distinct phenomena as such, but states: hunger, thirst, a full colon or bladder, the position and arrangement of our limbs and body parts.
Unsensed are the rest of the spectrum: infra-red, radio, ultra-violet, x-rays, gamma-rays. Infra- and ultra-sounds. Magnetism. Radiation. The weak and strong nuclear forces. The smells of air and water. What trust tastes like, or the pitch of democracy.
Another huge part of our input isn't direct but is indirect -- the reports of others, including sets of models by which we construct a grammar for the Universe: there is me and you and them, there is here and there. There are dogs and cats and lions and bears. There are bacteria and viruses, and electrons, and protons, and quarks. And moons, planets, stars, solar systems, and galaxies. All of which are constructs we've assigned, to those shadows on the wall of Plato's cave. Some more useful than others, but all wrong, in at least part. Some are even, perhaps, psychologically or physiologically innate to our brains.
And from this assemblage -- reason, sensation, pre-assembled models, we assemble our picture of the Universe, and query it, checking at times to see if what's visible out there, through what we can see, or think we see, actually corresponds with what we'd thought we'd see.
Which returns us to the dilemma you posed: what happens when that outside verification doesn't match our internal world-model? Do we reject the observation, or the model? Do we bend each? Do we even recognise the discrepency?