Why prove to a man he is wrong? Is that going to make him like you? Why not let him save his face? He didn't ask for your opinion. He didn't want it. Why argue with him? Always avoid the acute angle.

During my youth, I had argued with my brother about everything under the Milky Way. When I went to college, I studied logic and argumentation, and went in for debating contests. Talk about being from Missouri, I was born there. I had to be shown (Missouri is the "Show Me" state). Later, I taught debating and argumentation in New York; and once, I am ashamed to admit, I planned to write a book on the subject.

Since then, I have listened to, criticize, engaged in, and watched the effects of thousands of arguments. As a result of it all, I have come to the conclusion that there is only one way under high heaven to get the best of an argument – and that is to avoid it. Avoid it as you would avoid rattlesnakes and earthquakes. Nine times out of ten, an argument ends with each of the contestants being more firmly convinced than ever that he is absolutely right.

You can't win an argument. You can't because if you lose it, you lose it; and if you win it, you lose it. Why? Well, suppose you triumph over the other man and shoot his argument full of holes and prove that he is non compos mentis. Then what? You will feel fine. But what about him? You will have made him feel inferior. You have hurt his pride. He will resent your triumph. And –

A man convinced against his will
Is of the same opinion still.

Real salesmanship isn't argument. It isn't anything even remotely like argument. The human mind isn't changed that way.

- Dale Carnegie
How to Win Friends and Influence People, p. 112.