Sources should be independent of the subject. For example a person's webpage is not usually acceptable source. Ideally sources used in Wikipedia are published by reliable, third-party publications known for fact-checking and accuracy such as:
Adding information from scholarly books and articles is important for creating a accurate Wikipedia article that is notable and includes the most up-to-date scholarly information and sources.
Newspapers will cover topics that often can't be found in scholarly sources. They'll have more current coverage of on-going events. They'll often have information about people, as well as obituaries which can be an essential source for a Wikipedia article.
