The strongest form of learning has always included a social element, that is, being able to share the learning experience and possibly expand one’s understanding through social contacts. This sharing is valuable even if it is with other learners or people whose understanding is not at the same level as one’s own.
The guidance of a teacher is even more valuable to the learning experience, to be able to clarify and extend one’s own learning by developing new insights prompted by or inspired by a good teacher or subject matter expert.
Many, perhaps most, times a teacher is unavailable, or the teacher is available, but the learner doesn’t have the resources to access that teacher. Independent study to mastery is absolutely possible. But the journey to mastery is easier and often more rewarding with the guidance of a teacher.