All claims must be supported by a book, website, or news organization independent of the subject of the article. The source must be reliable, meaning it cannot be a blog, MySpace page, or personal website. This makes it difficult, if not impossible, to prove that an inaccurate statement is true, and that it should stay in the article. The policy regarding this states that the statement has to be verifiable, not necessarily true. See
Wikipedia:Verifiability for more information.