Bilingual people always have a ‘dominant’ language. It is nearly impossible to perfectly master several languages at 100%. We always sacrifice a little bit of a language to gain in ease in another language.
According to Psycholinguistics Professor François Grosjean ‘language forgetting is simply the flip side of language acquisition and (…) it is just as interesting linguistically’. In a paper published in Psychology Today, he also explains how bilingual children may learn and forget several languages in a life-time. This is interesting and echoes with my own experience. As a child I learnt, forgot and relearnt French; learnt and forgot Spanish, learnt English. As an adult, I am now learning Italian and hope that a trip to Ecuador, where I acquired Spanish in the first place, will give me the opportunity to reawaken it!
I think it is my own learning and forgetting which motivates me to teach others.