The urban organism auto-regulates*, in this way, its own development, tapping into a repertoire of solutions already experimented with that become adapted, when necessary, to new exigences. The role of the planner revolves, therefore, around the "collective memory"**, historical and cultural[,] of urban civilization that while renewing itself and evolving always maintains a strong relation of continuity with the past. In contrast to the planner, who checks the validity of the projected idea on the basis of rational analysis of how it responds to the context and to its impact on the future development of the urban organism, the organizing solutions of the collective memory are legitimated by their proven historical efficacy: they are the result of a selection protracted in time. This characteristic situation is at the same time a measure of the power and the limits of the organic city: if on one side it is capable of adapting itself with great flexibility to changing circumstances, on the other side its effective capacity to adapt depends essentially on one factor: the absence of traumatic discontinuity within the external conditions. ...In the presence of a context radically altered, and therefore with exigencies and problematics thoroughly new, which require a creative radical effort and therefore the search for organizing solutions entirely original, the capacity for self-organization of an organic city goes into crisis, and the danger of chaotic degeneration becomes concrete (emphasis mine).I suggest any of you who can read Italian get this book: it deals expressly with a subject that urban theory has only implicitly dealt with in the Anglosphere.
* He suggests replacing this translation with self-regulates.
** Cf. Carl Jung.