The emergence of the preference is a complicated process, made even more complex by: the potential diversity of the criteria to be considered the fact that the criteria are not independent from one another the difficulty of measuring them (they are perceptions, not ‘objective’ facts) the dynamic evolution of the perceptions over time the non-linearity of the functions linking some of the criteria to the preference (sigmoidal curves, parabolic curves, etc.) the fact that it is impossible to formalise these links by a classical preference function (additive model), as one single factor may trigger opting-out. In other words, it is a system.