The threshold for inclusion in Wikipedia is verifiability, not truth. There are two important consequences to this. The first is that sometimes things that are true cannot be included. The second is that sometimes things that are not true are included. The second of these is often infuriating to those who know the truth. It means that Wikipedia is wrong.

While at first glance that may appear like a very big problem for Wikipedia, in reality it is not. In fact, it can be seen as a good thing. Wikipedia is a project to build a free encyclopedia. Encyclopedias are tertiary sources and Wikipedia is no different in that respect. Tertiary sources collect knowledge that has already been published in what are called secondary sources. Tertiary sources do not generate new knowledge but rather just reflect what is already known and has already been published on a topic. If what has been published is incorrect, then these errors will be replicated in an encyclopedia. It is not until secondary sources are published which correct these errors, that these corrections will be reflected in encyclopedias.

In a general sense, a stream cannot rise higher than its source. So too with Wikipedia.

In simple English, Wikipedia editors can basically use anything that has a source and is considered credible. And anyone, of any age, can edit Wikipedia. Even though Wikipedia is a tertiary source, it is unlike an encyclopedia in the regard that a professional pool of researchers compile what are considered facts in an encyclopedia. In contrast, Wikipedia's editing is open to anyone, and if a subject is popular, it is biased to the majority (contemporary) opinion of Wikipedia editors. Editors who revise the Wikipedia articles can also place information that is false or subjectively inappropriate.

• Wikipedia:Wikipedia is not a reliable source
• Verifiability, not truth in action, a real example of Wikipedia having factually incorrect information, but verifiable information
• Caveat lector