"Truth is not what you want it to be; it is what it is, and you must bend to its power or live a lie." - Miyamoto Musashi
In 1995, neuroscientist Edward Adelson published something known as the checker shadow illusion, shown below. In this optical illusion, square A appears to be darker than square B.
Yet in actuality, squares A and B are exactly the same shades of colour; the screen pixels are identical, demonstrated below. If you're not convinced, try using your fingers to mask out all the other squares.
On first impression, squares A and B appear to be different shades of colour, yet they are verifiably the same shade.
The Brain Predicts The Truth
There are several explanations for the checker shadow illusion; let's stick to a simple one.
When you initially see the checker board, your brain predicts that all the squares will either be light or dark. The reason it makes this prediction is that for every other checker board you have seen in your life, such as checkers gaming boards, chess gaming boards, and checkered patterns on the street, there are only two different shades of colour, light and dark. Yet in the checker board illusion, the presence of the green column and its shadow creates the presence of three different shades - light, dark, and something in-between light and dark (we'll call it grey, although strictly speaking all three are shades of grey). Outside the shadow created by the green column, the seemingly dark squares are actually grey. Inside the shadow created by the green column, the seemingly light squares are actually grey. Squares A and B are grey.
Our brain constantly makes predictions about the real world using an inner model of the world that we have been creating and modifying since birth. This inner model relies upon the subjective context of previous experiences to interpret new situations that it occurs in reality - when a new checker board pattern is encountered, subjective experiences of old checker board patterns, all of which had two different shades of colour, are brought forth into our mind's eye and imposed upon reality. The older we get, the more these impositions or predictions actually mask true reality; we actually "see" our own predictions, not what actually exists right in front of our eyes.
To put it simply, as we get older the more we hallucinate our realities. The only exceptions would be a small child who has not yet created any complexities in their inner model of the world, or perhaps the extremely aware individual who has worked diligently for years or decades to perceive the truth beyond the subjective faults of their predictions.
Don't get me wrong - using an inner model of the world to make predictions about that world is a great strength and the source of true intelligence. The inner model can constantly be refined and improved, leading to better predictions and more successful interactions in the real world. The ability to make better predictions about a thing compared to someone else equates to greater intelligence regarding that thing compared to someone else. The true nature of intelligence is the primary, essential reason that the concerns of certain people fretting about computer-based artificial intelligence posing an existential threat to mankind lack a sound basis. Computer systems make objective calculations about reality; they are reactive. Brains make subjective predictions about reality; they are proactive. True intelligence lies not in the former, but in the latter; actualization of the singularity, in which computer-based artificial intelligence surpasses human-based intelligence, is at least one hundred years away.
But I digress. My point here is that despite the brain's powerful prediction-based intelligence, sometimes the predictions get in the way and lead to false conclusions about reality that, just like the checker board illusion, are really, really hard to identify - even when someone else points them out using objective data.
The Heart Knows The Truth
How do we know what is real when our own brain is prone to imposing its own preconceived predictions upon the world, hallucinating reality before our eyes? It can help to have someone point them out using objective data, yet that is not always an option as there are some things in life we must discover for ourselves.
It's a tricky question, and I'm not sure how to answer it. Yet it may be best to discover what our heart says. If we are in tune with our heart, it will not - cannot - lie to us. The heart will radiate the truth even as we chase the faulty aspects of our predictive inner model, as we see dark and light where there is only grey.
The Japanese swordsman and calligrapher Miyamoto Musashi summed this up as follows (1):
"Even if you strive diligently on your chosen path day after day, if your heart is not in accord with it, then even if you think you are on a good path, from the point of view of the straight and true, this is not a genuine path. If you do not pursue a genuine path to its consummation, then a little bit of crookedness in the mind will later turn into a major warp. Reflect on this."
Our own brain can lie to us for years or even decades, culminating in serious imbalances in our perceptions of reality; not so our heart. It's not important that your brain thinks it is doing the right thing, it's important that your heart knows you are doing the right thing - even if, sometimes, it makes "no sense" to your brain and its predictions. The sense is there, but the brain can't see past its predictions to perceive it.
To find the truth, search your heart...search within.
References (1) Musashi M. 1645. The Book Of Five Rings.