How should you behave when someone is teaching a third-party something you know to be wrong?

Andy, I know exactly how you feel. ^_^ I think it really depends on the situation, and the person. Some examples: If you hear a total stanger acting like an expert - why bother? Let them continue to think they are smart. Eventually it will trip them up. If it's a colleague or a friend, you may want to correct them in a gentle way, i.e. saying "I think that may mean XYZ, not ABC - that's what I have heard" etc etc. Not outright saying like "you are wrong SUCKER!" and bashing them over the head with a rolled up newspaper, even if you feel like it. If you're with other people you may want to bring it up later, if it still nags at you. If someone challenges you on something though and you are convinced they are wrong, I think it's ok to be more assertive with your opinion, since they are the one who instigated the challenge. It's always good to be polite though. You can follow those general principles in private online exchange (e.g. email or messaging) also I  think. However, in a public online forum, e.g. Quora, if someone is asserting a totally wrong opinion or statement as fact (i.e. the first scenario above), and you just know it's wrong, then I think it does a disservice to people who are reading it if only the 'wrong' statements stay up. You may end up upsetting the other party in the process, but in that case you have to weigh whether you want to upset one person you don't really know, vs. a whole bunch of people you don't really know. At least this is how I generally operate. (Although at some point it gets too exhausting to keep contradicting people too. In which case I just shrug it off and leave it be. Some people just do not want to be told they are wrong, even if they are wrong.) I also strongly believe that the sagest people are the ones who know when to say they don't know about something and are not afraid to admit it. There are a disturbing number of people who just don't want to admit they don't know something though. People who pretend to know everything after experiencing something for only a short time, or shallowly, are generally not worth bothering with.

The reason why we sometimes feel uneasy about correcting people seems to be that we don't want it to be done to us.  It feels good to be an authority on anything, and it feels bad to be a newbie.  The asker appears to be sensitive to this, and don't want to hurt anyone's self-esteem.   Counter-intuitively, about half of the human population (Jung’s “Thinking” types) is eager to be corrected.  Individuals in this group might argue back when we correct them, but they do not feel any displeasure.  Contrary to what many of us (Jung's "Feeling" types) believe, the argumentative "thinkers" are simply trying to improve their "answers" to the problems at hand, evaluating the various possibilities on merit/evidence.  Even when they are forced to conclude that they are wrong, they do not feel stupid--and for that reason we don't have to worry about their self-esteem much when disagreeing with them.  Ironically, when we do succeed in teaching them something, Thinking types may actually gain respect for our intellect, be grateful for our honesty, and start to identify with us as their comrades.  If instead we don't correct them when we should, we can cause them to feel that we are not open to intellectual exchange on an equal basis (collaborative learning) and are closed to debate.  In short, we'd look snobby (i.e. know-it-all). The best way to correct someone is to simply phrase everything as "we" instead of "you."  let's do an experiment: let's go back and read my answer after replacing all the "we" with "you," and try to detect the difference in tone.  See the difference?  If we phrase suggestions in a cordial way, and if we don't take argumentation as a sign of disrespect, then we don't really have to care if the audience is composed of Thinkers or Feelers.  We'd be able to freely express ourselves.   :)

It sounds like you almost get angry about it. That's not a good starting point for politely/socially correcting someone. In the "stop! I don't understand" example the corrected will lose face if you straight up came out and said "no, it doesn't" (or a variation of that). Maybe you'd get into an argument about it, and no matter what you'll easily come across as a jerk. Instead say: "Another way to say it that I like is abc. What you said can be understood as [whatever it means]". The idea is to engage in conversation and be helpful/interesting than just correcting. (If you have role power (you are the boss) or you are a teacher/mentor I'd suggest just correcting, but do it privately).

When people share their 'knowledge' of their experience of something, in this case living in China as an expat, it's just their opinion.  And everybody has a right to their opinion, no matter how wrong they are.  lf you are part of the conversation, l would just add ' ln my opinion (stressing the opinion word) ...............and then state what your perseption would be. However, when we are talking about facts, these need to be corrected.  l would try something along the lines of  'l think you may have misunderstood what you were being asked.  The correct way to say that would be.............'

You just mentioned the reason I hate to read the popular press on any subject I am even a moderate expert on... they are ALWAYS wrong. But you can't stop people from sharing ignorance and/or prejudice I am afraid. For why, see the http://en.wikipedia.org/wiki/Dunning%C3%A2%C2%80%C2%93Kruger_effect The best you can do is present a cogent argument for why they are wrong, then walk away hoping the third parties heard/considered it.