Pluralistic ignorance
In social psychology, pluralistic ignorance is a situation in which a majority of group members privately reject a norm, but go along with it because they incorrectly assume that most others accept it. This is also described as "no one believes, but everyone thinks that everyone believes". In short, pluralistic ignorance is a bias about a social group, held by the members of that social group.
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.