Being at a loss for words is never ideal for a journalist, yet the mind-numbing massacre of 132 schoolchildren in Peshawar has left me struggling.
I can think of only three occasions during more than four decades as a journalist when I've experienced a similar inability to find the appropriate words: the Hillsborough football stadium disaster in 1989, when 96 people were crushed to death; the Rwanda genocide in 1994, when an estimated 800,000 people were slaughtered in a matter of weeks; and the 9/11 attacks in New York and Washington, in which nearly 3,000 people lost their lives.
It's not just the numbers that freeze the brain; it's something much more fundamental than that. It's the sense that this simply should not be happening; it is not how the world was meant to be; it is, in all senses, appallingly, horribly wrong.
When children lose their parents, they are called orphans. When a spouse dies, the survivor is called a widow or widower. Yet we have no word to describe a parent who loses a child, because - at least since the advent of modern medicine - it is just not meant to happen.
It's not only the words I've been struggling with. I have also been trying to imagine the mindset of someone who conceives, and orders, such a murderous attack on schoolchildren. And if that's hard enough, how much harder it is to imagine what's in the minds of the men who actually pull the trigger, who see the children cowering, hear them screaming in fear, and shoot nonetheless.
To try to understand is not the same as trying to excuse. No one should ever seek to excuse the cold-blooded, deliberate mass murder of children. But without trying to understand, we have even less chance of finding a way to prevent more such ghastly attacks.
So here, hard as it is, is my attempt to understand. The Pakistani Taliban, or Tehrik-i-Taliban (TTP), who said they were responsible for the Peshawar attack, claimed it was in response to Pakistani army attacks on their bases in north Waziristan, which borders Afghanistan. The school, they said, was used mainly by army families and was therefore a legitimate target for a revenge attack.
According to a spokesman, the attackers were under orders to kill only boys over the age of puberty. Even if that is indeed the case, and we have no reason whatsoever to believe it, it would seem the gunmen flagrantly disobeyed their orders.
But suppose some of the gunmen had seen members of their own families killed by army strikes. Suppose some of the casualties had been children (which is almost certainly the case, as tends to be the way with such operations). Would that enable us to understand better the brutality of the counter-attack?
I don't think so, even if - and again, we have no reason to suppose this is the case - the gunmen were indeed from the areas where the army has been in action. In fact, some of the survivors are reported to have said that the attackers spoke Arabic or another non-local language - possibly Uzbek - which suggests that they were anything but local.
So what about the shadowy figures who conceived and planned the attack, the Taliban leaders thought to be hiding out across the border in Afghanistan? (Incidentally, the border between Pakistan and Afghanistan, the so-called Durand Line, named after Sir Mortimer Durand of the Indian Civil Service, is in many places almost entirely a work of fiction.)
For them, as for their Afghan counterparts, with whom they share an ideology but not a common leadership, the goal is to smash the authority of the central government and carve out an area where they can rule unhindered, in accordance with their own traditions and beliefs.
There's also a well-founded suspicion that some of them are backed, if not sponsored, by elements deep inside Pakistan's military structure, who share at least some of their aims (weakening the civilian government, destabilising Afghanistan, keeping India on its toes). We may assume, I think, that even if that were the case, they would draw the line at slaughtering the children of fellow military personnel.
On Thursday, though, the man accused of being the mastermind behind the attack on the Taj hotel and other targets in Mumbai in 2008, in which 165 people were killed, was freed on bail by a court in Rawalpindi. I'm not at all sure what we're meant to make of that.
This is the region where more than 100 years ago Britain and Russia were engaged in the Great Game, vying for dominance in a strategically crucial area of central Asia. The tragedy is that so little has changed. Afghanistan, Pakistan and India are still caught up in - and players in - the 21st Century version of the same brutal game.
The 132 children of the Army Public School in Peshawar who died in last Tuesday's attack were its latest victims. They will not be the last.
Does any of this help to explain why they were killed? Not really. I suspect nothing can.