It is a sound working hypotheses to assume that those internal
of a user called 'knowledge' or 'mental model' are
responsible for the
way a user is 'interpreting' his perceptions, is organizing
and is selecting his 'actual actions'. Furthermore is the
correspondence between the mental model and the real world
an important factor for the number of occuring failures caused
The mental model of a user can not directly be observed; it has to be reconstructed by observable facts as a hypothetical theoretical model which serves as an interpreting model of the behavior of a user.
The mental model is highly dynamic; it has to be constructed by sequences of certain actions ('learning'), but it can again 'fade away' ('forgetting').