A "lightly" negative consequence of this deficiency is the fact that, faced with a given external reality, almost any person makes a personal image-model associated with that external reality. We will see later that, for extreme situations, such deficiency is associated with the psychiatric disorder called "paranoia". The symbolic models do not have such problems. Once a symbolic model is made in a mathematical environment, the "law of the propagation of the errors" is able to predict the importance of any element or relation. For instance, if we have a complex mathematical formula, the law of the propagation of the errors will tell us how much the result is changed if an element is changed with, let's say, 1%. We already used the term "correct" associated with the importance of an element or relation in an image model. If there is an external reality and two associated models, one image-model and one symbolic-model, and if the two models have the same predictions, then the importance associated with the elements and relations of the image model is correct. If not, the right importance is that of the symbolic model. The above method is not good in any practical situation. In fact, there is no method to know if we associated the right importance to any element or relation of an image-model. This is XD4. XD5: this deficiency is a technological one. It means that there is no hardware or software method to erase a model of the brain. A model is made forever. It can be destroyed only in an uncontrolled way due to the biological deficiencies or the brain. The consequence of this deficiency is huge in many practical situations. The problem is developed more in another section of this book. THE STRUCTURE OF THE BRAIN, THE PSM MODEL The Protection and Surviving Model (PSM) is the basic image-model of any brain. When a new being is born, it has only this model in its brain. This model is very complex and it will be described in this chapter. There is a section of the PSM, which contains a collection of short-range models. They have to act very fast to provide minimal protection for that being (including newborn beings) in some specific dangerous situation. These activities are called "reflex actions". The PSM contains also some basic models, like the model to keep in the eyesight a moving entity from external reality, or the model to touch by hand an entity in the range of the hand. There is also a collection of models associated with equilibrium and the general stability of the external body, together with a model of it, of course. There are also a number of long range models which contain the instincts to survive unconditionally, forever (basic design requirement). During the period of growing, others models can be included in the PSM, models which are associated with the educational process. Such models have to prepare the being to live in a specific external reality.