Occasionally we encounter people who make statements that we know are factually wrong. A guy asked the sage Nasrudin, “What is two plus two?” and he replied, “six.” Then the guy said, “You’re wrong! Two plus two is four.” And Nasrudin said, “No, I’m right. We do math differently where I come from. By the way, if you knew the answer in your system why did you ask me in the first place?” In the Spanish language we call that number quatro. Aren’t all these names for numbers arbitrary? Well, yes, the names are largely arbitrary across languages, and some numbers are avoided in some languages, like the number four sounds like “death” in Cantonese, Chinese so it is considered a bad number. Not to get too much into number theory, but we must be aware that the names and the shapes of the numerals are largely arbitrary, but the underlying concepts are fixed. Nasrudin was exercising his bizarre wisdom in his answer to the question. He commonly does things like that in his folk tales, and frequently there appears to be a deep meaning in his seeming stupidity.
But my more common question is, How should we respond to people we know are wrong? How, when we know positively they are wrong, at least by the conventions of the common language that is being spoken at the moment? I believe this should be approached from the Trustworthiness of Information Chart which has 15 levels of trustworthiness defined. 
Click chart for a bigger view. Most information we deal with on a daily basis is in the mid range, near TST-7 and is trustworthy for daily social interactions; the material that is near TST-0 has no testable proofs and no accountability, but offers considerable comfort when considering unsolvable problems that generate fear. The high numbers like TST-11 and above are where the persons presenting the information will be held personally accountable for the accuracy, and therefore the information is probably accurate. So when we are encountering problems with trustworthiness in the high numbers we should offer clear-cut testable proofs for the accuracy of our information. When we are in daily conversation and our interlocutor makes an error of fact, or even of judgment, most of the time we should respond with our personal knowledge of the facts as we understand them to be, without recourse to documentation or scientific deniability tests. However, when dealing with the lowest assertions of truth based on ancient hearsay statements that have been spun into good stories, we should doubt the truthfulness of the facts of the story and pay attention to the message being communicated by the story. With these we should consider and challenge the applicability of the message to our present situation, and avoid the questions of fact, because there is no fact that can be discussed, only the application of the story.
Probaway - Life Hacks 