[jvb1000]

I hate this adage. I've taught, a lot. At universities, in high school, and to adults. The idea that people who can't do can teach is not remotely true. Most people can't teach effectively. If you can't do something you also probably can't teach.

[cal85]

I think there’s a strong grain of truth in it when it comes to “business skills” or subjects in that general area.

[rrrrrrrrrrrryan]

It's because business skills are mostly learn-by-doing skills. No matter how many books you read about bicycle riding techniques, you're not going to ever be able to do it unless you've actually given it a try and scuffed your knees a bit.

Not all skills are like this, of course - you probably want your doctors and scientists to be people who actually read the textbooks and paid attention to their professors.