The cognitive bias called "curse of knowledge" is when you have so much information on a topic, that some topics may be difficult or even impossible to discuss, with someone who does not have the same background as you.
As a teacher it can be difficult to properly explain things to a student, that require a lot of background knowledge.
Some patients will find it difficult to understand their illness, not because their doctor doesn't know what is wrong, but because it is explained in a framework the patient doesn't understand. Years of medical school does make a difference and getting diagnosis can lead to a lot of changes.
From my own experience, the best teachers I have had, have been able to explain things in multiple ways. Repetition alone is not enough, but with a different perspective on a topic, it becomes easier to understand.
When time permits, a teacher can explain things from a student perspective or build a frame that is well understood by the student.
Certificates of achievement, doctorates, bachelors and many more are examples of acquiring background knowledge.
Many will at some point in their life acquire a driving license. This often requires some level of study and a practical exam. Through these experiences they build a shared background knowledge, which others can use to easily identify those who know (and what they know).