To sing with other people and for other people, that's when you can really learn something about your voice. You can only learn so much if you create your own boundaries all the time. But then, other people can really teach you something. You know, if you're trying to sing with them, or if someone brings a style.
Some people see teachers and they associate the feelings of the other students who are present with the teacher. They psychically connect with all those hundreds of minds and they don't key to the teacher at all.