[theknightwhosaysni-NI]

It's true that you don't need to be an expert to teach things, especially when writing free content on the internet.
This is because in any given field, the everyday man is not interested by learning things at an expert level. Most people want to learn things in fields where they are beginners.

The more deep and complicated the content is, the more targeted and narrow the audience will be.

If you teach things at an expert level, you're going to be interesting for the very few people who already have a well advanced knowledge in this field.
If you teach things on a more basic level, the audience is going to be much wider.

I think it's true for any field. Wether it is physics, learning a new language, learning a new habit, or even personal development.

Take physics for instance. If an expert decides to give Phd level classes for free over the internet, it's likely that his audience will be very narrow, due to the complication of the courses.
On the other hand, if one decides to make articles with pictures and easy explanations about the latest discoveries of physics, much more people will be interested in reading the material.

I'd even say that it's a challenge for experts to make their content accessible to a wide audience.