“Heraclitus called self-deception an awful disease and eyesight a lying sense.” – Diogenes Laertius, Lives of the Eminent Philosophers, 9.7
Diogenes Laertius was a biographer of philosophers. One who recorded was Diogenes of Sinope (don’t ever confuse your Diogeneses). The latter, the story is told, walked around Athens during daylight holding a lamp, and looking for an honest man.
Heraclitus was a pre-Socratic Greek philosopher. While he believed that all things were a product of fire, he also held the opinion that all things are in flux. As Plato writes:
Heraclitus, I believe, says that all things pass and nothing stays, and comparing existing things to the flow of a river, he says you could not step twice into the same river. (Plato Cratylus 402a = A6)
This played into Heraclitus’ position on knowledge. Due to the flux of the experiential world. He does not claim that we cannot know, but he does claim that most don’t learn what they should be learning. His words ring true today, that people are focused more on gathering information than understanding it.
Knowledge of self is no different. If we spend our time experiencing without understanding the experiences what good are we? As our senses are that which gives us an experience we must ensure mental awareness of these experiences. Everything we consume defines who we are, and if everything is in flux then we must be aware of these changes to the outside world and ourselves.