Why is it important to have a native speaker teacher or friend?

I am mother tongue Italian, and I started studying English when I was six years old. I love this language and its sound, and I often envy those who speak and understand it perfectly.
I teach Italian to international students, and I teach English to Italian students, and in my heart, I know that the best teacher is a native speaker, even though a wise English teacher told me:
"The best teachers are not necessarily native speakers. They are those with knowledge and passion".
Yes, he is right...but only native speakers know the rules and the stress for correct pronunciation.
They are familiar with idioms, expressions, and common sayings...
I know we can't always have a mother tongue teacher, but in 2021 it is easier to be in touch with new friends or colleagues with whom we can test ourselves.
How often do we discover that a verb or a word can have several meanings?
Yesterday I learned that "do you copy me ? "means ….can you hear me? That's incredible for a non native !!!! I'm still laughing.
Even though I started studying English at the age of 6, I take lessons with a mother tongue teacher. Every day I listen to videos or podcasts, and I try to learn and steal all their secrets...but..no way! Maybe one day ...ha ha ha!
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