Twenty years ago, when your computer had a problem, it would notify you with
?SN ERROR IN LINE 5740. The World Wide Web has improved little in this respect.
Page Not Found (HTTP 404) The page you are trying to access does not exist.`
Some have whimsically described
HTTP 404 as a kind of signal that you have dropped off the edge of the world; in reality, the 404 is actually more like an “access denied.” It is a signpost signifying the boundary of the real universe, forbidding passage. Additionally, the HTTP 1.1 specification states:
“This status code  is commonly used when the server does not wish to reveal exactly why the request has been refused, or when no other response is applicable.”
So the server does not wish to reveal why it returned the error; that would explain the rude brevity. But as to Reasons Why, there are several possibilities, each of them intriguing and philosophically revealing.
1. The file never existed
What we have here is a genuine, undeniable attempt at Creatio Ex Nihilo, an unsatisfiable demand for a piece of information which does not exist. Although, technically, it may actually exist in some alternate location, you did not request it from that location; you requested it from here, and it does not exist here.
Short of actual thought, bits of magnetic polarization on a hard disk platter may be the most pliable, easily manipulated information medium known to man; but even using such a lightweight ether, it is unreasonable to expect a missing page to be spontaneously created from nothing.
2. You mis-typed the URL, or the page has moved
If you suspect that this is the case, you are probably in the midst of a silent struggle against Fate. The scent is warm; you know the information you seek exists and is somewhere nearby; but in your search you have come up against a wall. Fate is unaccountably fond of allowing you within a hair-breadth of success, sometimes without your realizing it…and then turning you aside at the last instant. I really should not aid you in a struggle against Fate, as it may adversely affect the outcome of some of my own similar grapplings; but as a gentleman, I should at least point you to some point of reference, from whence you will be able to continue your search.
If you arrived from a link on another site, however, the cause is most likely…
3. It once existed but has since been deleted
In which case we can only say, Requiescat In Pace, and wishfully surmise that it probably wasn’t worth seeing anyway. The extinction of information through obsolescence is a natural part of life just as much as the physical degradation of leaves, people and stars—the difference being that the dead information does not actually provide nourishment to the information that comes in its place, merely a little extra space for storage.
We should in fact, be grateful that although the link that led here is now useless, someone responsible for the page that was supposed to be here has noticed its irrelevance and cleaned it up. So in one sense entropy has increased and in another sense it has been, in some measure, controlled. The second law of thermodynamics is an inscrutable beast…in any case, we are now one step closer to the heat death of the universe.
4. You are hunting for hidden web pages by typing spurious URLs
The probability of this being the case is admittedly infinitesimal, but there are people in these times who do such things. And if true, it reveals something about you, namely that your skin is yellowing under the influence of your flourescent lighting and your computer screen, and you have a need of fresh air. Do you realize that even the possibility of your being able to waste your time in such ways without starving to death is a historical anomaly? It is against nature, and it will take its toll.
Perhaps the next time a terse error code is flung your way by a miserly machine, you will pause to contemplate the dim mythos of modern communication, the transience of life, and how they may affect your own traipsings upon the boundary between the physical and the intangible. But for now you’d probably better be going. You have wasted enough time already.
“It is absurd to divide people into good and bad. People are either charming or tedious.”
— Oscar Wilde (1854–1900), Lady Windermere’s Fan, 1892