There are an implicit set of rules and mores that governs online discussions; by implicit, one only learns them through trial and error because there is no guide, until now.
Avoid declarative statements – otherwise you risk appearing pigheaded – a cardinal sin – versus just mistaken. This is probably the most important rule. Unless you can quote directly from a trusted source, such as Wikipedia, use use hedging language. Even for statements that seem incontrovertible, such as the seemingly self-evident pronouncement of the earth being spherical, can still trip you up. Instead of saying ‘the world is round’, which can be countered by someone correctly pointing out it’s an oblate spheroid, write ‘the early is roughly spherical’. Instead of writing ‘vitimins are useless because they leave the body undigested’, replace with ‘there is some evidence vitamins may leave the body partially digested, reducing their possible effectiveness’. There, now the pro-vitamin people are less likely to get mad because you leave the possibility open of being wrong, which doesn’t occur if you only make declarative statements.
Another example, ‘Modern culture, science and arts originated from 17-18th cent. France and Germany’ should be ‘I (believe, think) (a lot, some, parts..etc) of the sciences, arts, and culture came from France and Germany, but other regions (may have, probably) contributed’. Someone can counter your declarative statement by saying it was the Scottish Enlightenment, which is technically correct because Scotland did give us Hume and Adam Smith – but anyway, the person who corrects you will be praised (karma, points, etc) and you will look like a buffoon even though you were mostly correct, but done in by making a declarative statement.
Tell stories. A reason why Obama, Clinton, and Reagan won is because their campaigns conveyed empathy and trust though personal narratives and stories, not just facts and figures, most of which are quickly forgotten.
Avoid rhetorical, lazy or loaded statements, also known as begging the question. Questions such as, ‘Have you stopped beating your wife?’ or ‘How did XYZ happen?’ (if the cause of XYZ is obvious enough that it immediately lends itself to an answer, suggesting intellectual laziness to pose the question) are examples.
‘No good deed goes unpunished’ While ignorance is bad, so to is coming across too helpful or too smart, to the extent of sounding pretentious and pedantic. If you try to pass yourself off an an expert and unwittingly give bad advice (falling victim to the Dunning–Kruger effect), may God have mercy on your soul.
Misunderstandings. Missing the author’s point (if the comment pertains to an article) or misconstruing the argument of someone else are both grave offences. Missing the point is possibly worse than making trolling, off-topic posts because people have little patience for ignorance that could lead the innocent astray, while trolling remarks can simply be ignored. Moderators will delete the obvious troll posts, but the misunderstandings tend to stay up because they are on-topic and not trolling, making it the community’s job to debunk the bald faced ignorance.
Seldom use superlatives. IF you are too confident you may fall victim to Dunning–Kruger, and rather than consider your point, people will immediately look for counterexamples to disprove your superlative. Instead of saying, ‘the best investment for XYZ’ say, ‘this investment may be a good idea for XYZ, your mileage may vary’.
Intellectual laziness, including but is not limited to: logical fallacies, any of the aforementioned items on this post, failure to read between the lines (misconstruing the author’s point), reductionism (oversimplification of something abstract), making a hasty judgement (shooting from the hip), and counter-exampling (giving a single, trite counter-example to try to refute a lengthy, complicated thesis – typically a sign of intellectual laziness in the more nuanced social sciences).