How do we know what we know?

[Aegon]

Human consciousness is a survival tool, not meant to figure out the truth of reality. We're not hardwired to see things as they really are, but rather hallucinate a reality which benefits our survival the most. It's crazy shit, innit? The idea that our brain gets sensory input and just puts out its best guess as to what it going on... insanity. I don't think this is a controversial statement, since we all learn in high school physics that there are various waves that are not visible to our brains like the visible color spectrum is. Then on the quantum level, we know that the act of observing particles is enough to change them. This then begs the question: can we really know anything to be objectively true if everything we do passes through such imperfect filters as our senses? If the answer is no, then is there even a point in thinking about it?

What can we confidently say is objectively true and true independent of the human experience? How much can we confidently say is true and how much are we assuming is true for the sake of our collective sanity?