"Those who can, do. Those who can't, teach." This adage is heard whenever someone wants to disparage teachers. Some defenders try to disprove or discard the saying. Personally, I believe it is mostly correct and should be used to honor teachers.
For me, "Those who can, do" means that people who have a natural talent express it easily through endeavors:painting, music, mathematics, engineering, counseling, gardening, whatever. Someone who handles difficult tasks without much effort is usually a topnotch performer, but not necessarily a good teacher of the trade.
Earl Scruggs, a musician, invented a style of three-finger picking that has spread across the world and is known as Scruggs-style banjo. He is, of course, one of the best purveyors of that style, but his book on how to learn it is not very good. Perhaps people with some natural affinity for the skills needed find the book useful, but it is not a good learning tool for the majority of pickers. It demonstrates how Earl plays songs and has an excellent history of the instrument, but offers no clues about overcoming difficulties while learning. I suspect Earl had few problems and thus can offer few solutions.
Pete Wernick wrote an excellent tome on bluegrass banjo. He is a good writer and has a Ph.D. so he knows the many ways people learn. But I suspect he also had problems learning to pick. Those insights helped him write a first-rate teaching guide.
For myself, I used to be tone deaf. After years of effort, I conquered the syndrome and can play and sing reasonably well. I am also good at teaching melody since I had so many problems learning it. Students get multiple ways of figuring out a tune and calculating the best way to play it on the banjo. But after hearing me at a jam session with rock and rollers, one of my students asked how to syncopate a backup rhythm. I showed him but when he couldn't follow, I was stuck. I had no tricks of the trade, no secrets, no alternative approaches. Rhythm is felt and I'd only worked on my ear so I couldn't offer a solution.
Albert Einstein, the physicist, is often offered as proof of both a doer (Nobel Prize) and a teacher (excellent books on relativity theory). The pundits overlook the fact that the thought experiments dealing with the relativistic effects of high speeds were difficult for Einstein. He spent many hours contemplating them, working through the ramifications. Once he solved the problem for himself, he was able to help others get past the same dead ends he encountered.
There are probably some people with natural talent who are also talented teachers. I suspect teaching itself may be an innate talent. However, I don't believe a trained educator with natural teaching ability can teach any subject using a workbook. But someone with journeyman level skills in an area and experience in solving problems inherent in learning the associated tasks is a much better teacher than a highly talented professional with no skills for explaining the many tiny steps involved in learning.
Those who can't naturally do but persevere anyway with a strong desire to master a skill can probably teach us all a thing or two about learning, working through difficulties, slogging through the low points of life. I remember coaches saying, "Ya gotta want it." People with natural talents don't want in the way the rest of us do. They can easily master a skill. But luckily for most students, "Those who can't, teach."