Sounds like your friend is an amazing tutor. Communication and teaching is indeed hard. I really believe most people don't learn math because they don't get th

Sounds like your friend is an amazing tutor. Communication and teaching is indeed hard. I really believe most people don't learn math because they don't get the teaching they need, not because math is somehow cognitively inaccessible for them (except in case of low iq). Lots of people learn language and grammar and are able to write strong texts with a high level of rational and logical thinking, but have not been able to learn math. These people clearly have the mental faculties for math, they just didn't get the teaching they needed. Math is a language for expressing thought, just like any language is, and these people have mastered other languages, so they have the prerequisites for being able to learn the language of math. Math is an especially hard language and it requires good teaching.