The prediction of the evolution of external reality (see general theory) is the main requirement of design for the human or animal brain. Thus, this requirement is fulfilled by the facility of the brain to build and operate models.
ETA 2: Truth, reality, and communication
Any result of the simulation on a model is a truth associated to that model. As pointed out in the general theory, a truth is associated by us to a symbolic message (generated by a symbolic model); however in order to keep the terminology simple, in the case of image models, a result obtained by simulation on the model is also called 'truth', in spite of the fact that it is used 'as is', without the necessity to explain it.
Example: If an animal builds an image model of the external reality, predicting a dangerous situation, it is possible to find the solution to the problem by simulation on the model. This solution (the truth) might be, e.g. to flee. The truth will activate directly the preexistent action model, which is in this case to flee.
We'll refer from now on only to symbolic models. If no model is specified, any truth is nonsense.
Example: The truth is ãa car crashed into a wall". This truth might be generated by any of the following models: -accident -test -movie/cartoon -computer game
In any of the above models, the specified truth is interpreted differently (it has a different meaning).
The theory underlines thus, that the model which generated a truth needs to be specified and accepted before the presentation of the truth. This basic requirement is always met in positive sciences.
In common life, the declaration of the model is not always done, and often the model does not even exist in an elaborate and coherent form. Emerging from here a long line of conflicts between individuals, groups or cultural zones, which all have their own reality associated to the same external reality. This can be interpreted as a design deficiency of the brain. Some can compensate this hardware deficiency by software, e.g. the individuals situated on level 3 of consciousness (see the general theory).
There is a fairly common situation in external reality when a person states a truth, and then builds the model to support it. This happens usually for persons based on image models only, and when they interact with external reality, they only translate the image truth to a symbolic truth. Such persons are recognisable by their rudimentary logic and their tendency to fragment any discussion to particular sections of the external reality. Such persons can't discuss a single general subject.