The roots of the phrase are much deeper than that. It goes to our (rather unique) American anti-intellectualism. I’ve been hearing it for eons from people who are uneducated. I’ve heard it even after I became educated from the same people. It makes people who haven’t gone through the rather difficult process of getting an education feel better about themselves because they have all this “common sense”. It’s the same “common sense” that results in a lot of people “...knowing what ain’t so.” Yes, there are some engineers (scientists, doctors, tax accountants, etc) that are better than others. But what they all have in common is that they have been educated. Even the good engineers aren’t uneducated.

In education...especially higher level education...teachers teach as well as “do” work in their fields. Even primary and secondary educators have to undergo constant training in their subject so that they stay relevant. And we require that they do that on their own dime while paying them a pittance.

Finally, for those who use the saying, go out and try to teach someone how to do what you do. It’s not all that easy. It really does help to have “done” what you are teaching. I’ve been teaching people how to work on bikes for the last 15 months in a class setting and for the last 10 years in Fix Your Bike hours. It ain’t as easy as just “doing it”. I can fix most anything on a bicycle in a few seconds to a few minutes. Teaching someone how to do something takes a whole lot longer and takes a lot more effort.