An identifier is much like an assertion, an opinion, or a thought; its only reality comes from what you, I, it, they, or we believe. Belief is based on "authority", often established by such things as trustedness of the witness (e.g., a family member to identify a victim) or weight of numbers (e.g., everyone agrees that song is ...). Communicating authority in the digital world is imperfect. After clicking on a URL, you are returned exactly what the web server asserts is bound to it, whether that be the page you expected, a page you didn't expect, or a "not found" error. Web servers act on behalf of their owners via complex processes that can distort the exact sense of authority intended. Servers are often not maintained or managed as you expect, returning results that you, the owner, or both would consider incorrect.