Wikipedia:You don't have to cite that the sky is blue
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Some people think that every single assertion in an article needs to be cited. That is not true, not even for an article that is a Good article or Very Good article candidate. That is called overcitation. The result of this is that these editors recommend other editors spend more time citing things that are considered by some not controversial.
Something only need be cited if it meets one of the following criteria:
- direct quotations,
- published opinion,
- counter-intuitive or controversial statements that are challenged or likely to be challenged, and
- contentious material relating to living persons.
Otherwise, it generally doesn't need to be cited.