Grosjean argues that there has been a monolingual bias regarding who is considered a 'bilingual' in which people who do not have equal competence in all their languages are judged as not speaking properly. 'Balanced bilinguals' are, in fact, very rare.
According to Grosjean, the definition of "bilingual" has been skewed towards those with equal fluency across all their languages. Individuals who don't possess equal competence in every language are often deemed to speak improperly.  The concept of a truly balanced bilingual is rare.