In such situations the common notion of proportionality between inputs and outputs of a system is incorrect. Conversely, the regime shift concept also emphasizes the resilience of systems – suggesting that in some situations substantial management or human impact can have little effect on a system. Regime shifts are hard to reverse and in some cases irreversible. The regime shift concept shifts analytical attention away from linearity and predictability, towards reorganization and surprise. Thus, the regime shift concept offers a framework to explore the dynamics and causal explanations of non-linear change in nature and society. Regime shifts are triggered either by the weakening of stabilizing internal processes – feedbacks – or by external shocks which exceed the stabilizing capacity of a system. Systems prone to regime shifts can show three different types of change: smooth, abrupt or discontinuous, depending on the configuration of processes that define a system – in particular the interaction between a system's fast and slow processes. Smooth change can be described by a quasi-linear relationship between fast and slow processes; abrupt change shows a non-linear relationship among fast and slow variables, while discontinuous change is characterized by the difference in the trajectory on the fast variable when the slow one increases compared to when it decreases. In other words, the point at which the system flips from one regime to another is different from the point at which the system flips back. Systems that exhibit this last type of change demonstrate hysteresis. Hysteretic systems have two important properties. First, the reversal of discontinuous change requires that a system change back past the conditions at which the change first occurred. This occurs because systemic change alters feedback processes that maintain a system in a particular regime. Second, hysteresis greatly enhances the role of history in a system, and demonstrates that the system has memory – in that its dynamics are shaped by past events. Conditions at which a system shifts its dynamics from one set of processes to another are often called thresholds. In ecology for example, a threshold is a point at which there is an abrupt change in an ecosystem quality, property or phenomenon; or where small changes in an environmental driver produce large responses in an ecosystem. Thresholds are, however, a function of several interacting parameters, thus they change in time and space. Hence, the same system can present smooth, abrupt or discontinuous change