Undesirable stability. Stability is commonly thought of as desirable, for its presence enables the system to combine of flexibility and activity in performance with something of permanence. Behaviour that is goal-seeking is an example of behaviour that is stable around a state of equilibrium. Nevertheless, stability is not always good, for a system may persist in returning to some state that, for other reasons, is considered undesirable. Once petrol is lit it stays in the lit state, returning to it after disturbance has changed it to "half-lit" - a highly undesirable stability to a fireman.