We are complicated creatures who spend our lives trying to simplify the world in which we live. We seek out patterns. We do it without even knowing it. Our brains are pattern-matching all the time.
Life offers us constellations of random dots and instinctively we try to join them - to see some unifying picture, to find some underlying pattern that makes sense. If we didn't, we would be overwhelmed by information and sensation; it would all become so much white noise.
When American Airlines Flight 11 hit the North Tower of the World Trade Center on the morning of September 11, 2001, the only thing that made any sense to those who witnessed it was that they had just seen a devastating accident.
Then United Airlines Flight 175 hit the South Tower and everything just stopped making sense.
In the decade that has elapsed since that day, the footage of that impact has been played and replayed. Who has not seen it many times over? Yet still some gap remains between what we see and what we can honestly claim to comprehend, to make sense of.
The attempt to bridge that gap presses more keenly with each passing year, each anniversary, and provides a unifying theme on the following pages.
In the decade since 9/11, enough books to fill hundreds of libraries have been written on the subject. Thousands of hours of investigations have been conducted. The greatest thinkers of our time - and, indeed, the most plodding - have expounded their theories in attempts to find understanding, to bring closure, to assign blame, to make sense, to simplify.
But, 10 years on, are we any closer to doing so?
Two thousand, nine hundred and seventy-seven innocent people, and 19 hijackers, were killed in the attacks. An estimated 116,000 or more - soldiers, civilians and insurgents - have died in the subsequent military actions in Iraq and Afghanistan. A figure for the number of civilians killed in US drone attacks in Pakistan is harder to come by.
Yet despite our ability to measure the human consequences in such visceral detail, there is still no true international consensus over what happened, why it happened or even who made it happen.
Still, we search for meaning. Still, we search for a pattern that fits. Still, we get it wrong. We try to simplify our world and instead manage only to render it more complicated. We try to make it safer and we end up making it more dangerous. The international response to 9/11 did just that, the politics of fear breeding mistrust and fostering misunderstanding between cultures, religions and countries. Sometimes, eventually, we get it right. Consider the slow, frequently painful gestation of the 9/11 memorial, which opens on Sunday, the 10th anniversary of the calamity. It marks, as Saul Austerlitz writes, "an endpoint of sorts to the eternal present tense of the attacks".
And, through the use of an algorithm to group the names of the lost by associations of life, service and death, rather than alphabetically, it also fulfills our all-too-human craving for order; a pattern of sorts is imposed on the chaos of Ground Zero.
The 10th anniversary has no significance beyond our curious need to recognise temporal milestones - markers on our way to a better understanding of the past, or at least a place at which to pause and consider. The 25th anniversary will come, then the 50th and then the 100th.
However imbued with significance we might want this milestone to be, it is too soon to talk of legacies, or endings. However much we might wish for it, it is too soon to draw grand conclusions or to discern a pattern that makes sense of it all.
For now, all we can say is that the world is different because of 9/11 and the world is different in spite of 9/11. Ten years on, it remains as simple and as complicated as that.