Wikipedia:There is no Book
It is human nature to want to do things "by the book", to follow the rules to make sure everything goes proper. However, on Wikipedia, we do not want our contributors to have to learn or memorize a set of rules before editing. Hence, Wikipedia does not have firm rules, as described in the Five Pillars, our policy against bureaucracy and even the paradoxical policy against rules.
A problem occurs if some editor assumes that a certain rule exists, and insists that people follow it even if that rule does not in fact exist.
Nevertheless, sometimes editors insist that a certain issue "must" be dealt with via a certain procedure because that'd be common sense, even if they cannot find a single Wikipedia page that explains that procedure or that sense. In effect, they insist that people "play by the rules" regardless of the fact that they just made up those rules themselves. You cannot do things by the book when there Is No Book.