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.
Ignorantia juris non excusat
Ignorantia juris non excusat or ignorantia legis neminem excusat (Latin for "ignorance of the law excuses not" and "ignorance of law excuses no one" respectively) is a legal principle holding that a person who is unaware of a law may not escape liability for violating that law merely because one was unaware of its content.