The phrase “Those who can do, those who cannot teach” is more a phrase to dismiss teachers than to provide useful guidance. The original meaning was intended to instruct students not to become too fixated on ivory tower teachings and put more emphasis on practical experience. It is true that most teachers of economics are neither businessmen or millionaires. There was a time when most of the latter did not have college degrees. A new recruit with a freshly minted college diploma working for a boss with a high school education was often something of a nuisance; a “mansplainer” in modern parlance. So “those who can do, those who cannot teach” was a comeback phrase to mean “Snap out of your mansplaining and learn from the job”.
But as society changed and everyone became more educated, this phrase became a disparage of teachers rather than a put-down on the superficially educated. Teaching is a noble profession and being taught is a fruitful experience. The world is in constant need of more and better teachers. At the same time, what really makes you an expert is the act of putting in ten thousand hours of experience. We should understand that teachers are the people who guide us through the maze so that we can make the best of those ten thousand hours.
The act of teaching is an education unto itself. Helping others to write helps you focus on your own writing skills. Both Kurt Vonnegut and John Irving taught creative writing courses before they became best selling authors. As I browse through Youtube, Skillshare, and Patreon courses on writing, I see many talented instructors who could become tomorrow’s best selling authors. In that respect, those who teach today may become those who do tomorrow.
There is also the question of what it is that you are trying to accomplish through teaching. For example, the objective of teaching economics is not always to make millionaires, or even successful businessmen. You do not need to know how to write code in order to use a computer, and you do not need to know the structure of transistor circuits to learn how to code. Computer programmers who learned their craft at vocational schools learn only to write code and have minimal education on the physical principles of the semiconductor, while those with formal education are forced to spend time absorbing hours of lectures on the atomic structure of the microscopic switch. Such detailed knowledge on the esoteric background of a subject may or may not be useful in the daily application of programming skills. But it is meant to enhance the foundation over which our daily skills are built on. So, do the teachers who lecture us on the atomic structure of integrated circuits know how to program computers? Perhaps not. Are they unnecessary? That is debatable.
My father was past forty when he bought his first personal computer. It was an 8-bit computer that ran on a Motorola CPU and worked off an operating system called CP/M. There were almost no prepackaged software on the market at the time so he hired a computer developer to help him with his programming. When he asked the developer what was the most efficient way to learn about programming, the developer answered, correctly I must add, that it was impractical for a middle aged doctor who could afford to hire a developer to do his own programming. Since computers were evolving so quickly, whatever he learned could become obsolete by the time he mastered it. Instead, he should learn the mathematics behind the programming, which would prove much more durable. and that is how my father got into studying the Bayes’ theorem back in the 1980s.
A great teacher once told me that some lectures only need to reach just one student in the class. Knowledge is sometimes like sperm sprayed over an ovum. Only one needs to make contact. And out of a thousand fertile eggs cast into the ocean, if only a few mature enough to create the next generation of eggs, the breeding is a success. We are now all aware of the concept of the meme, and how knowledge and ideas tend to spread in a manner similar to that of the virus. But viral contagions do not only spread exponentially. They sometimes lay dormant and barely survive in small numbers, until conditions become favorable to their sudden explosion which becomes a base number from which they slowly dwindle down until they once again are reduced to minimal survival levels waiting for the next big opportunity. We have seen ideas of bigotry and tyranny behave this way. But enlightenment, civilization, technology, and all forms of progress have also behaved this way, evolving through fits and starts, experiencing near extinction on multiple occasions. But usually surviving just enough to pass on to the next generation. Sometimes, teaching is a part of that process.
Teaching is a multi-faceted process. You can teach practical knowledge to put bread on the table, you could teach the basics behind the practical knowledge to build a more stable foundation, you could teach knowledge that is more profound and thus more durable than the practical skills that could become obsolete in a shorter span of time, you can teach to plant a seed for the civilization to come, or you can teach in order to learn yourself. Teaching is a multi-faceted process because learning is a multi-faceted process. A large part of what you learn will be practical skills to put bread on the table, but a large part of what you do to put bread on the table will be repetitive and dull work. The more durable parts of your knowledge will be the parts that are less immediately applicable. And the part most important for the future of mankind will probably be the part that only a few people will ever listen to.
Should you teach? If you can, yes probably. But you should never lose sight of learning. And you should be conscious of what level of teaching you are involved in.