In a nutshell: "Articles must not take sides, but should explain the sides, fairly and without editorial bias. This applies to both what you say and how you say it."
More details: "All encyclopedic content on Wikipedia must be written from a neutral point of view (NPOV), which means representing fairly, proportionately, and, as far as possible, without editorial bias, all the significant views that have been published by reliable sources on a topic."
Neutrality is about "due weight", so that better supported views receive more attention, and some receive none at all
The earth is flat (conspiracy)... though the conspiracy has a separate article about it
Astrology predicts personality and events (pseudoscience)... though the article details rich mythology and history
Verifiability states, in a nutshell: "Readers must be able to check that any of the information within Wikipedia articles is not just made up. This means all material must be attributable to reliable, published sources."
Verifiability continues: "Verifiability means other people using the encyclopedia can check that the information comes from a reliable source. Wikipedia does not publish original research. Its content is determined by previously published information rather than the beliefs or experiences of editors. Even if you're sure something is true, it must be verifiable before you can add it.
Verifiability means that the claim being verified comes from a Reliable Source. What makes a source reliable?
"Base articles on reliable, independent, published sources with a reputation for fact-checking and accuracy. Source material must have been published, the definition of which for our purposes is "made available to the public in some form".
Good sources tend to include books published by respected publishing houses, established magazines, academic papers, mainstream newspapers, university textbooks, or authoritative trade journals.
Self-published sources, website forums, blogs, press releases, and social media posts are rarely considered reliable, except as sources on themselves.
A third-party source is not affiliated with the event, not paid by the people who are involved, and not otherwise likely to have a conflict of interest related to the material.
Any exceptional claim requires multiple high-quality sources.
Articles about living peoplerequire reliable sources.
If no reliable sources can be found on a topic, Wikipedia should not have an article on it.
Robust review, specific support: "In general, the more people engaged in checking facts, analyzing legal issues, and scrutinizing the writing, the more reliable the publication. Information provided in passing by an otherwise reliable source that is not related to the principal topics of the publication may not be reliable; editors should cite sources focused on the topic at hand where possible. Sources should directly support the information as it is presented in the Wikipedia article."
Nutshell: "Wikipedia does not publish original thought. All material in Wikipedia must be attributable to a reliable, published source. Articles may not contain any new analysis or synthesis of published material that serves to reach or imply a conclusion not clearly stated by the sources themselves."
Details: "Wikipedia articles must not contain original research. The phrase "original research" (OR) is used on Wikipedia to refer to material—such as facts, allegations, and ideas—for which no reliable, published sources exist. This includes any analysis or synthesis of published material that serves to reach or imply a conclusion not stated by the sources. To demonstrate that you are not adding OR, you must be able to cite reliable, published sources that are directly related to the topic of the article, and directly support the material being presented."
If you thought it or studied it but never formally published it, it's original research.
If you are making a new conclusion from two other pieces of fact that don't make that particular conclusion, it's original synthesis.
Editors are here to summarize, not reveal new truths from their own experience.
Editors are not empowered to create new narratives, or a new thesis, argument, conclusion, or perspective that isn't present in underlying reliable sources.
There are things you just know as an expert or from personal experience that Wikipedia will still require a reliable source for.
Credentials, reputation, expertise, or other markers of prestige and rank do not matter for editors; however, they are essential for the published, independent reliable sources they cite.