Just because you've used lots of software doesn't mean you can write code. Just because you've been in lots of buildings doesn't mean you can be an architect. And just because you've logged a million frequent flyer miles doesn't mean you can fly a plane.
But if that's all ridiculously obvious, why do some people believe that just because they've taken classes, they can teach? (Or just because they've read lots of books, they can write one?) The problem isn't thinking that they can do it, the problem is thinking they can do it without having to learn, study, or practice.
I'm amazed (and more than a little disheartened) how many people believe that simply by virtue of their being skilled and knowledgeable in something, they're implicitly qualified to communicate, mentor, teach, or train that thing. It devalues the art of teaching to think that because you've been a student, you can teach well. That because you've experienced learning, you can craft a learning experience.
She goes on to say that having a PhD may not be necessary, but you can't just wing it. She goes on to list Eleven Things to Know and Ten Tips for Trainers.
As a teacher, I appreciate the fact that someone recognizes that it requires something more than subject matter knowledge to teach. The current trend in federal regulations and state teacher licensing seems to only concern itself with that subject matter stuff, and I think a teacher needs more than that in order to be successful. As a professional, I am continually upgrading my skills and my knowledge -- both about my subject matter and about pedagogy and human behavior and lots of other things. I take this very seriously, as do most teachers I know.
I advise you to check out her post if you haven't yet.