I was talking to a mental health professional (don't remember her credentials) about JWs. Part of what I couldn't get my brain around was how JWs (myself included, when I was "in") can seem to function so well in other areas, but so easily and completely give up their minds to others when it comes to the Org. The behavior seems so irrational and deluded, with so many cognitive distortions at work, that healthy functioning in other areas would appear precluded. Then the prof told me about two interesting phenomena.
Encapsulated (Compartmentalized) Delusion - A delusion that usually relates to one specific topic or belief but does not pervade an individual's life or level of functioning.
Folie à deux - (literally "a madness shared by two") is a rare psychiatric syndrome in which a symptom of psychosis (particularly a paranoid or delusional belief) is transmitted from one individual to another. There have been occasional claims of shared visual hallucinations that are near, to exact, duplicates. The same syndrome shared by more than one person may be called folie à trois, folie à quatre, folie à famille or even folie à plusieurs (madness of many).... Folie à deux and its more populous cousins are in many ways a psychiatric curiosity. The current Diagnostic and Statistical Manual of Mental Disorders states that a person cannot be diagnosed as being delusional if the belief in question is one "ordinarily accepted by other members of the person's culture or subculture". It is not clear at what point a belief considered to be delusional escapes from the folie à... diagnostic category and becomes exempt because of the number of people holding it. While a large number of people may come to believe obviously false and potentially distressing things based purely on hearsay, these beliefs are not considered to be clinical delusions by the psychiatric profession and may be labelled as mass hysteria. [emphasis added]