The brain is often thought of as an organ dedicated to carrying out careful rational analysis of everything that concerns our survival. However, when we investigate a concept called reversible thinking , we see that this is not the case. To exemplify this, we can use a little game.

I’m gonna show you four different cards. On each of them, on one side there is a number and on the other side there is a letter.

And I also want you to know that I am convinced that on every card with an “E” on one side, there is a “2” on the other side .

Now I ask you: How can you tell if I am telling the truth? What minimum number of cards do you need to turn over to find out if my statement is correct or false?

Before reading further or going out to find the solution to the problem, take a few minutes to think about it… And remember your answer well.

Playing with thought

If you think that in order to know if my statement is correct or not, it is necessary to turn over the card containing the letter “E”, then you have responded like the vast majority of the people who were posed the problem.On the other side of the card with the letter “E” there may or may not be a number “2”. If not, then you can be sure that my statement is false.

But on the other hand, it turns out that if you do find a number “2”, that’s not enough to assert that my statement is true.Now, you will probably conclude that you also need to turn the card with the “2” on it to see if there is an “E” on the back. But that solution is also wrong .

In the event that there is a letter “E” behind the card that has the “2” on it, we will know for sure that the statement I made at the beginning is correct. But on the other hand, remember that I have not said anything about what should be behind the card with the “2” on it, and you can find, strictly speaking, any of the many letters of the alphabet. What if we also turn over the card with the letter “N”?

Well, I think it’s clear that this solution doesn’t make any sense.The problem is solved satisfactorily by turning over the cards that have the “E” and the number “5”.You can understand why, can’t you?

But that’s outrageous. I have to explain everything!

Reversible thinking

Clearly, first you need to see if there is a “2” behind the card marked with an “E”. But we must also sniff out what is behind the card that has the “5” on it, because only then will we know without a doubt, in the case of finding an “E” on the other side, that the premise I formulated at the beginning is true.

Let’s look at it another way. If behind an ‘E’ there can be a ‘5’ which would spoil the statement, it is legitimate to think that behind a ‘5’ there can also be an ‘E’ which, for practical purposes, is exactly the same.The possibility of reasoning in one sense and also in the opposite sense is known as reversible thought , and it seems to be a property that tends to be scarce among the specimens of the human race.

When we believe something, what we usually do is look for information that confirms our belief , and we rarely take the trouble to look for the counter-proof, in case we are wrong.

We make quick, hasty, almost unthinking judgments, and as soon as some indication appears that we are right about what we thought, we immediately conform; this is a phenomenon that occurs every day, and as incredible as it may seem, from which practically no one is exempt, from the individual with the lowest possible educational level to the one with the highest academic honors.

You don’t believe me? I’m going to tell you about a series of studies that have shown the thought process that doctors follow when making a diagnosis.

The first hypothesis is the one that wins

Imagine that you go to see Dr. Gonzalez. At the office, to the typical question of “What brings you here”, you tell him about a series of problems that have been bothering you for some days. As is natural in this case, the doctor takes note of the symptomatology that you refer to him and begins to think of one or two hypotheses that could explain the problem.Based on this diagnosis, which the doctor estimates as probable, he performs a brief physical examination and indicates a series of studies.

Well, scientific evidence suggests that in cases like this, doctors cling to their original hypothesis , dive headlong into confirming it, and often lose sight of the need to find the counter-proof that validates the diagnosis (the equivalent of turning over the card with the number “5”).

But it’s a little more serious than that.What has been observed is that doctors (even experts, who have many hours of clinical experience) tend to dismiss data that do not meet their expectations , underestimate them, or sometimes even ignore them completely.According to the very nature of the brain, any clinical picture a patient may present cannot be assessed objectively and absolutely. Beyond his knowledge, the physician makes an interpretation of what the patient tells him, and establishes in his mind a starting point on the basis of which he asks for the studies he considers necessary.

The problem is that many times this original diagnosis works as a rigid and immovable anchorage point.The professional then tries to find data to confirm his previous opinion. In the process, he may even overestimate any minor or irrelevant evidence that goes in the same direction as his previous expectations, giving it a high degree of confirmatory value while, at the same time, taking weight away from any information that is not consistent.

When we hold on to expectations

I am not suggesting that the reader should not visit his doctor the next time he catches the flu or feels any pain. Nor am I suggesting that you should lecture him on how to do his job. But the truth is that there is practically no subject concerning the human species that psychologists have not put their magnifying glass on at some point in history, and the subject of reversible thinking is one of them.

And this is how clinical reasoning often works . The first diagnosis that comes to the doctor’s mind determines the path to follow, and also contributes to distorting the interpretation of the results of the different studies that he or she requests from the patient. Something similar occurs with most people, regardless of their occupation, in their daily life and in their personal relationships.

All this irrationality that tints the senses and plays such an important role in everyday decisions is attributable, in part, to the fact that the brain is a cognitive sloth . This means that it is governed according to a principle of mental economy that often leads us to make mistakes in our day-to-day assessments.It is an invisible, unconscious process through which the complex is simplified, and helps us to create mental categories in order to classify our experience so that we do not have to start from scratch every time we are faced with a new situation.

It also induces us to take shortcuts in our processes of reasoning and drawing conclusions; all, of course, with the laudable purpose of making things easier for us, but unfortunately with the additional cost of a certain little madness or irrationality in our behavior.

Therefore, it is convenient to demystify the brain and not to consider it a supercomputer designed to perform detailed data analysis according to conventional logic. Whenever it can, it uses resources to take work off its shoulders.