Plato’s cave analogy concludes that one’s perception of reality is, in fact, their reality; because one cannot perceive anything outside of their reality. Perception is variable, and therefore nothing is truly absolute or can be proven.
Descartes asserts, “Only pure knowledge known by resources of reason can be reliable.” Then one might argue that reason is learned based on situation and environment, which changes for each person.
Every person perceives each situation differently. Therefore, the reason is also variable. What anyone can know is derived from information gathered and observation of the world. Then used to draw a widely agreed upon conclusion, but since what we know comes from what we observe and what we can observe continues to progress, factors multiple, and the prior knowledge expands, changing what one thought they knew.
Consequently, what one can observe and claim to know now and what one may “know” will differ. No one can ever honestly know anything, and one only knows what they believe to be true until they obtain new information and realize that they no longer know what one thought one knew.