"What!?! That's heresy! Mr. Andrews, how can you tell us that a good example is NOT the best teacher! We have been hearing that all of our lives, and now you want to tell us it isn't true!"
Yes. It isn't true.
The good example by itself is often not where the teaching takes place. You can be the best example possible, but if the student doesn't understand the reason behind what you are doing, or the process behind the doing, or why they should want to do that thing, then the example is largely wasted effort. The meaning of your example too often sails right over their head!
Special note to parents: Do you say "I will teach my child to be moral and ethical by my good example." This is a necessary but not sufficient condition for teaching values. You have to ACTIVELY teach why you are behaving that way. Teach what is the benefit to a moral and ethical person. What is the payoff to the student?
If you are not moral and ethical, then your active teaching of these values will very likely be ignored. Thus, the good example is important as a follow-up to the actual teaching.
A good example is useful when the student has grasped the underlying principles of the lesson. It mostly acts to polish or "lock in" the lesson already taught. The good example shows the student how to do the thing. It makes it real for him. He can emulate what you did, while at the same time gaining first hand experience-knowledge. It validates the teaching.
If I as a teacher model some good behavior, tool, method, or skill, the student may mimic it and be able to "parrot" it back to me. That is copying. That is being a human "tape recorder". That is NOT learning.
At best, "Teaching by being a good example" is passive teaching. The problem with it is that the actual learning must be done using the mental resources of the student, NOT those of the (hopefully better equipped) teacher!
Where does the idea of "A good example is the best teacher" come from? Why is it so common in the "folklore" of our society?
In the author's opinion it comes from people who either are too lazy or too busy to figure out how to teach that subject or who can't figure out how to teach it.
What is the likely reason they can't teach a thing? Most likely because they do not understand how to do it! An example is "how to think." It is not easy to do it correctly. Even it you are good at thinking, you may not know HOW you go about thinking! (Read the pages on thinking.)
Another example is how to debug or troubleshoot failed hardware or software (I am an engineer). There are engineers who are good troubleshooters. They can't tell you how they do it. They don't know HOW they do it! It is done mostly beneath their consciousness! I have seen it happen!
Scenario #1 (Passive teacher, great student)
A really intelligent student who is highly motivated becomes an "apprentice" to a capable person (a "Master" craftsman, be he a skilled tradesman, or an intellectual worker).
Eventually, the apprentice learns, develops, and
becomes a master of that trade.
Scenario #2 (Active teacher, great student)
Rhetorical Question: Which apprentice (scenario #1 or #2) will "Master" her trade sooner, and be better at it?
They both give up. (Sound familiar?)
Scenario #4 (Active teacher, student has fair to poor intelligence, unmotivated) (Sound familiar?)
Master may ignite a spark of interest. "I CAN do this!" In that case, the student will master the work better and faster.