This chapter explains the economic and social behaviour of either individual agents, or of groups of agents, by estimating its divergence from action rational in whole. Psychotic behaviour is rational because if the beliefs on which the behaviour is based were true, the behaviour would be the most likely means to produce the intended outcome without also producing side effects that outweigh its desirability. The psychosis may worsen under this regimen, and the agent deteriorate so much that no sign of strategy remains. In both the organic and functional psychoses, then, the agent's earlier limited area of irrational behaviour can develop into an extensive area of non-rational behaviour. This process of 'development takes place independently of the type of cause which produces it. Thus 'a neurophysiological disturbance' and 'a malformed strategy for coping with the agent's failure to attain certain end's are both characterizations of a story with one unhappy ending.