It is a characteristic feature of the victims of illusions and aberrations, that they develop an overwhelming faith in their erroneous ideas. There is nothing more difficult than trying to convince them – it need not even be hallucinations but only simple delusional, paradoxical ideas – that these thoughts are not valid. For instance when someone is convinced through his illness that he is being persecuted, it is impossible to convince him with sound reasoning that it is not true. Such a person can produce the most intriguing logical thought constructions to prove how real his delusional reasoning is. The human being can become obsessed with his delusions and firmly believe in the objective reality thereof.
Source (German): Rudolf Steiner – GA 62 – Ergebnisse der Geistesforschung – Berlin November 21, 1912 (p. 127-128)
Translated by Nesta Carsten-Krüger