Pluralistic ignorance
Pluralistic ignorance can be contrasted with the false consensus effect. In pluralistic ignorance, people privately disdain but publicly support a norm (or a belief), while the false consensus effect causes people to wrongly assume that most people think like they do, while in reality most people do not think like they do (and express the disagreement openly). For instance, pluralistic ignorance may lead a student to drink alcohol excessively because she believes that everyone else does that, while in reality everyone else also wishes they could avoid binge drinking, but no one expresses that due to the fear of being ostracized. A false consensus for the same situation would mean that the student believes that most other people do not enjoy excessive drinking, while in fact most other people do enjoy that and openly express their opinion about it.
Philippe Pinel
The fifth and last mental derangement is called idiotism, or otherwise known as “obliteration of the intellectual faculties and affections.” This disorder is derived from a variety of causes, such as extravagant and debilitating delight, alcohol abuse, deep sorrow, diligent study, aggressive blows to the head, tumors in the brain, and loss of consciousness due to blockage in vein or artery. Idiotism embodies a variety of forms. One such form is called Cretinism, which is a kind of idiotism that is relative to personal abnormalities. It is well known in the Valais and in parts of Switzerland.