Rational argument can be conducted with some prospect of success only so long as the emotionality of a given situation does not exceed a certain critical degree. If the affective temperature rises above this level, the possibility of reason's having any effect ceases and its place is taken by slogans and chimerical wish-fantasies. That is to say, a sort of collective possession results which rapidly develops into a psychic epidemic. In this state all those elements whose existence is merely tolerated as asocial under the rule of reason come to the top. Such individuals are by no means rare curiosities to be met with only in prisons and lunatic asylums. For every manifest case of insanity there are, in my estimation, at least ten latent cases who seldom get to the point of breaking out openly but whose views and behaviour, for all their appearance of normality, are influenced by unconsciously morbid and perverse factors. (...) But even if their number should amount to less than ten times that of the manifest psychoses and of manifest criminality, the relatively small percentage of the population figures they represent is more than compensated for by the peculiar dangerousness of these people. Their mental state is that of a collectively excited group ruled by affective judgements and wish-fantasies. In a state of "collective possession" they are the adapted ones and consequently they feel quite at home in it. (...) Their chimerical ideas, upborne by fanatical resentment, appeal to the collective irrationality and find fruitful soil there, for they express all those motives and resentments which lurk in more normal people under the cloak of reason and insight.
Carl Gustav Jung, The Undiscovered Self (translation of Gegenwart und Zukunft, 1957),
Routledge, London, 2002, pp. 2-3