Wikipedia:Verifiability: "Articles should rely on credible, third-party sources with a reputation for fact-checking and accuracy. ... The burden of evidence lies with the editors who have made an edit or wish an edit to remain. Editors should therefore provide references. If an article topic has no reputable, reliable, third-party sources, Wikipedia should not have an article on that topic."
Wikipedia:What Wikipedia is not: "Wikipedia is not an indiscriminate collection of information ... That something is 100% true does not mean it is suitable for inclusion in an encyclopedia. ... Wikipedia articles should not exist only to describe the nature, appearance or services a website offers, but should describe the site in an encyclopedic manner, offering detail on a website's achievements, impact or historical significance ... Wikipedia articles should not act solely as a summary of the plot of a work of fiction, but should offer comprehensive, summarised plots in conjunction with sourced analysis, offering detail on a work's achievements, impact or historical significance ..."
Jimbo Wales[1]: "I consider WP:V to be so central to Wikipedia that if there were ever a significant majority of contributors who wanted to do away with it, we would have an internal war on our hands that would make the userbox wars look simple by comparison. The important thing to remember here is that merely existing and typing in a web form does not make one a Wikipedian. The community is defined by the goal of the community, and people... no matter how numerous or vocal... who do not accept that goal are not a part of the Wikipedia community.."
Jimbo Wales[2]: "I really want to encourage a much stronger culture which says: it is better to have no information, than to have information like this, with no sources. Any editor who removes such things, and refuses to allow it back without an actual and appropriate source, should be the recipient of a barnstar."