There is a certain place that is unknown but to a very few, marked by nothing in particular but rumored to lie in hinterlands abutting some river town of no apparent note, which contains a great secret. It contains it in a real sense, as the secret is buried beneath that unmarked spot, many hundreds, if not thousands, of meters below the surface. The secret that is hidden beneath is an enormous cistern which, were one ever able to find the spot directly above it, manage to dig to its level, and penetrate its adamantine hull, one would take to be empty upon initial examination. However, it is anything but empty. It is, actually, quite full, but what it contains is not anything visible—nor detectable by any of the usual, scientific means. What it contains, what is nearly filling it, engages no external human senses and registers on no mechanical instrument. 
There are many myths which deal with the reality of human suffering. One particularly prevalent example is that of the “vengeful ghost.” Such a thing is the spectral remains of someone who died an unjust, often violent, death. That such a thing could happen—unjustly, so to someone who did not obviously “deserve” it—is something that strikes some universal and dissonant chord in the human psyche. It is simply unfathomable that the innocent truly suffer with no recompense, no revenge, no evening of the score: So the vengeful ghost is born, a spirit whose very nature is revenge, and whose fury and destruction are stayed only by the correction, as it were, of the death, usually in the form of the demise of the perpetrator—but sometimes, simple knowledge of the affront to balance and “fairness” is enough. 
Unsurprisingly enough, this is the genesis of the understanding that there is an “ultimate justice” after death. (I say “understanding” and not “belief,” because the reality of postmortem judgment has been known for some centuries by now, despite the objections of a handful of radicals.) Again, that a truly innocent person might suffer and die is a tragedy so incalculable that it has for millennia defied philosophers and theologians alike. The “imbalance” of such suffering is not, of course, the only sort of human suffering. Humans, it has been argued many times, were created to suffer. It is not the author’s opinion that so bleak an outlook can be completely justified, but neither can it be absolutely dismissed. Humans suffer and have been suffering for so long, that our suffering predates the word “our”—that is, we were suffering before we were even human.
Natural disasters—how many have been claimed by floods? Droughts? Heatwaves? Megatsunamis? Megafauna? Birth? and the like, over the 200,000 years of our physical modernity? Even in the 50,000 years of our behavioral modernity, which was the dawn of the human mind, such as we know it today, the dawn of an “us” which we would recognize as such? And of manmade disasters—how many souls have been harvested by war? Genocide? Infanticide? Suicide? Slavery? and torture unto death? The numbers are unknown and will forever remain unknown and to think upon them, to peer into the abyss, to listen to the chorus of endless screaming, immense beyond conception, would drive any normal human being to madness. The pain is too great. The loss, too profound—until the resurrection, many faiths claim, though current support for this is lacking. The apparent evaporation of all the horrors of human history, the darkness whose shine is unbearable, is not something which can be comprehended. The scales are, it would seem, tipped—but what seems is almost never what is.
The truth of the matter is quite different. The suffering of our kind does not evanesce away into some metaphysical void. It remains, as suffering, intact. Furthermore, it goes somewhere, intact, in the physical world, to join past sufferings in the great Cistern of Suffering, buried in the aforementioned, nameless hinterlands, behind that unknowing, blissfully ignorant town of no particular note. The Cistern collects and has been collecting since the dawn of suffering, millions of years ago. Human suffering, of course, is far richer, more expansive, more potent and dense, than the suffering of other animals. Our suffering could even be said by some to be “exquisite” in its heights and depths, and so the Cistern fills with the combined potencies of every conceivable variety of suffering, absolutely dominated by that of us. The Cistern fills and no one knows that it does or, more importantly, why. 
The few who know of it and care to speculate about its purpose offer few ideas, for they wish they could unknow of the existence of the Cistern. Some have said that it is a bizarre, cosmic counterbalance to the apparent disappearance (really, non-observation and forgetting) of suffering from its “rightful place,” which would be, burned into the human collective consciousness. Others have claimed that it has no purpose other than to collect that which is ineradicable. Were it not for the Cistern, they propose, the suffering would have “nowhere to go” and might go about the earth, causing more suffering—existing as some form of strange lifeform which subsists on creating more suffering and then integrating this into its body, were it really able to have such. The reality is that it is not known and likely will never be known what the true purpose of the Cistern is. 
The reality is also, however, that the Cistern is nearly full. Rough estimates, such as can be made, are that within the next century, the Cistern will reach its capacity. What is to happen thereafter? Is there another Cistern somewhere else which will begin to fill? No one knows of such, though there might be some other few who do, or who will be informed at some point of its existence. If this were true, would the process go on forever? Certainly, it could not, because there is only so much room underground, and the rate at which suffering accumulates is today accelerating far faster than ever before. Perhaps the Cistern will erupt, releasing its inconceivably gargantuan quantity of raw, human suffering. Heaven only knows what this would do to the humans unfortunate enough to be alive at that time. The result might be so catastrophic as to eradicate their very souls—all of them then alive on earth—which has only happened on a small scale, once before in human history, and the trauma inflicted on our species was so great that it has been mercifully erased from all memory. 
The Cistern fills. The hourglass runs low. The campfire around which we have been crouched for so long is going out, soon. Something truly terrible is coming and not a soul knows what it will be.