Why error 404 occurs?

[Paul]

Hi, I'd like to ask you a big problem that puzzles me, why error 404 occurs? Thank you for informing me by explaining clearly.

[Micah]

The HTTP 404, 404 Not Found and 404 (pronounced "four oh four") error message is a Hypertext Transfer Protocol (HTTP) standard response code, in computer network communications, to indicate that the client was able to communicate with a given server, but the server could not find what was requested.