1) What humans see is different than what they are looking at
Humans do not see a direct representation of external reality, but a translation formed by their eyes and mind. This is not some coffee house philosophical argument, but physiological fact. Human eyes and mind do a good but far from perfect job at detecting and processing light. When you are look at a bowl of apples or painting or mountain range, the image you see is not a direct representation of the objects, but a translation of limited sensory information made by your eyes and mind.
2) Many optical illusions are uncorrectable
Even after you learn that they are illusions and how they work, there are many visual illusions that still fool you. If you look at them the next day or two months later, they will still trick your eyes.
The mind contains compartments that perform specific tasks. For example, one compartment is used for comprehending spoken language, another for perceiving smell. Some of these compartments are isolated from other parts of the brain. These compartments sometimes are even isolated from conscious knowledge.
The perception of many visual illusions is made independent of your conscious knowledge. This explains why even your conscious knowledge that they are illusions does not solve your nonconscious misperception.
3) A human cannot determine the accuracy of its own mind
To humans, the reliability of the human mind cannot be known, because they use the human mind to test and judge the reliability. If your goal is to determine the accuracy of the human mind, that means you do not know the accuracy of the tool used for testing and judging (the human mind).
Your opinion about the reliability of the human mind involves a leap of faith. A common tendency is to overestimate the reliability. There are a number of reasons for this. One is that many cognitive errors and blind spots are unknown and not counted. Another is that a human’s belief system and worldview are premised on a reliable mind. If the mind’s reliability comes into question, so does the reliability of the belief system and worldview.
