the general writing/​presentation skills (including how to make things fun).
If you fail at the first point, you are likely to produce very popular but misleading explanations.
If you fail at the second point, you will produce texts that all experts on the subject will agree are fantastic, and yet the beginners will fail to understand them or to make the right conclusions.
If you fail at the third point, you will produce a great but kinda boring textbook.
The good news is that the second and third points are quite general, but they need a huge dose of genuine humility to listen to the actual experts and take feedback from them (especially when you know quite well that your text would be hugely popular even if you ignored them and just used your own opinion instead).
This may actually go against our status-related instincts (which might explain the relative lack of great exposition experts). On one hand, you have to treat the subject with great respect, to carefully avoid the possible misinterpretations, no matter how tempting they might be. On the other hand, the attempt to explain the subject to general audience in the most simple way, it feels disrespectful. Our instinct tells us that great wisdom requires great sacrifices to understand… and the goal here is precisely to communicate great wisdom with preferably no sacrifice on the side of the listeners (other than a little of their time).
For some people it may be psychologically painful to accept that others may learn in one hour a nontrivial part of what took them a few years of hard work to collect. It kinda makes you feel stupid.
I think it is a combination of three skills:
deep understanding of the subject;
knowing how to teach;
the general writing/​presentation skills (including how to make things fun).
If you fail at the first point, you are likely to produce very popular but misleading explanations.
If you fail at the second point, you will produce texts that all experts on the subject will agree are fantastic, and yet the beginners will fail to understand them or to make the right conclusions.
If you fail at the third point, you will produce a great but kinda boring textbook.
The good news is that the second and third points are quite general, but they need a huge dose of genuine humility to listen to the actual experts and take feedback from them (especially when you know quite well that your text would be hugely popular even if you ignored them and just used your own opinion instead).
This may actually go against our status-related instincts (which might explain the relative lack of great exposition experts). On one hand, you have to treat the subject with great respect, to carefully avoid the possible misinterpretations, no matter how tempting they might be. On the other hand, the attempt to explain the subject to general audience in the most simple way, it feels disrespectful. Our instinct tells us that great wisdom requires great sacrifices to understand… and the goal here is precisely to communicate great wisdom with preferably no sacrifice on the side of the listeners (other than a little of their time).
For some people it may be psychologically painful to accept that others may learn in one hour a nontrivial part of what took them a few years of hard work to collect. It kinda makes you feel stupid.