We already saw that any model evolves independently, by itself, based on the information taken from external reality or from others models. The aim of any model is to gain its stability. Once a model has a problem, it will continue to be active up to the moment when it regains stability.
There are some problems without solution. The model will continue to look for a solution forever. This activity can produce negative effects on the overall stability of the structure of models of the brain (it consumes a lot of energy).
The main problem without solution is death (human beings only).
This is a basic problem. So, there is a model which predicts the death of a person and that model has no solution to the problem. When there is no model to solve a problem, the PSM is activated. The PSM has no solution too and so it will make a specific model to solve the problem. But the new model has no solution either, and so, a dangerous loop is activated. This activity could be very dangerous for the stability of the structure of models of any mature human being.
Since the oldest times, the human beings found a solution: shielding models.
A shielding model is a model, which is made to prevent a normal model from activating the PSM and also to transmit to the model with problems some information to stabilize it.
The best-known shielding model is religion.
Observation: as a person becomes older and older, the prediction of death is more and more precise. The person has the tendency to become more and more religious. Also, when a population is under stress, it has also the tendency to become more and more religious.
A shielding model is associated to a normal model which has problems. A shielding model is not based on external reality. It cannot be included in a normal model, as the normal model cannot include a model which is not based on external reality.
The reality generated by a shielding model can be called "illusion".