What facts constitutes as citation-worthy
Generally speaking commonly known facts, such as things that appear in encyclopedias or even undergraduate text books don't need to be cited unless quoted.
But that doesn't mean &quot;known&quot; to everyone. If they are common knowledge among experts, for example, then no citation is needed.
If you quote or closely paraphrase something from a source, then you should cite that source.
But it is probably better to err on the side of over citation than under and citations can also sometimes help the reader, depending on the audience. A