From Modern Blacksmithing - J.G. Holmstrom 1901

In every profession and trade it is a common thing to hear beginners say: I know, I know. No matter what you tell them, they will always answer, I know. Such an answer is never given by an old, learned or experienced man, because, as we grow older and wiser we know that there is no such thing as knowing it all. Besides this we know that there might be a better way than the way we have learned of doing the work. It is only in few cases that we can say that this is the best way, therefore we should never say, I know: first, because no young man ever had an experience wide enough to cover the whole thing; second, it is neither sensible nor polite. Better not say anything, but simply do what you have been told to do.

Every young man thinks, of course, that he has learned from the best men. This is selfish and foolish. You may have learned from the biggest botch in the country. Besides this, no matter how clever your master was, there will be things that somebody else has a better way of doing. I have heard an old good blacksmith say, that he had never had a helper but what he learned some good points from him.

Don't think it is a shame, or anything against you, to learn. We will all learn as long as we live, unless we are fools, because fools learn very little. Better to assume less than you know than to assume more.

Thousands of journeymen go idle because many a master would rather hire a greenhorn than hire a "knowing-it-all" fellow. Don't make yourself obnoxious by always telling how your boss used to do this or that. You may have learned it in the best way possible, but you may also have learned it in the most awkward way. First find our what your master wants, then do it, remembering there are sometimes many ways to accomplish the same thing. Don't be stubborn. Many mechanics are so stubborn that they will never change their ways of doing things, nor improve on either tools or ideas.

Don't be a one-idea man; and remember the maxim, "A wise man changes his mind, a fool never."

Be always punctual, have the same interest in doing good work and in drawing customers as you would were the business yours. Be always polite to the customers, no matter what happens. Never lose your temper or use profane language. Don't tell your master's competitors his way of doing business, or what is going on in his dealings with people. You are taking his money for your service, serve as you would be served.