Losing Usain Bolt to athletics is like losing the air.
He is an elemental presence, the one figure capable of elevating a humble foot race to a midsummer blockbuster.
Now that he begins life today as an ex-athlete, his last race run, he stands to be missed more than even he, with his carefree Caribbean swagger, can comprehend.
He was asked at these London championships if we would ever see his like again. "No, I don't think so," he replied. "I'm unique."
From a lesser mortal, it might have been perceived as staggering hubris. From him, it was simply a statement of fact.
The moment of adieu was marked with a poignant gesture, as Bolt took to the track in odd-coloured shoes: one purple, one gold.Purple denoted the colour of his alma mater, William Knibb High School in Falmouth, Jamaica, where a teenage Usain described by his teachers as a "prankster" found his metier in life.
Gold defined his pre-eminence ever since: eight Olympic gold medals, world records galore, all securing him the helpless adulation of millions. "Forever fastest," read the message on his footwear.
We had better believe it.
His retirement marks a profound and solemn watershed in the history of track and field.
What now? Bolt has not even hung up his spikes, and already the sport can be in no doubt as to the chasm he will leave behind.
The past week's winning times for 100 and 200 metres - 9.92sec for Justin Gatlin, and 20.09 for Turkey's Ramil Guliyev - were the slowest on the global stage for 14 years.
And yet it is his stage presence, which has beguiled everybody from Barack Obama to female Swedish handball players, that athletics will miss most.
From gyrating with samba dancers in Rio to performing his 'To Di World' pose alongside Mo Farah, from high-fiving stadium mascots to hugging the hapless Chinese official who upended him on a Segway scooter, Bolt was never less than box-office.
Not even the finest biologists can fully explain why Bolt, whose 9.58 for 100m is more than two tenths of a second quicker than the next man who has never committed a doping violation - Maurice Greene, with 9.79 - came to be so fast. Some attribute it to his childhood penchant for yams, a highly popular food in his native Trelawny parish and one known to enhance the fast-twitch muscle fibres essential for sprinting.
Others contend that the Maroons, the escaped slaves who populated this rugged region in the 18th century, bequeathed to their successors a level of physical resilience from which Bolt has benefited.
Taking 41 strides to cover 100m when most of his rivals needed 44, Bolt saved athletics at a time when few realised it needed saving. He became supra-national, belonging as much to the world as to Jamaica.
Serena Williams spoke for many when she observed that when Bolt lined up for a final, she would find herself backing him as strongly as any representative of her own country.
"I can't think of anybody else besides Muhammad Ali who has captured the public imagination or a global audience like Bolt," Sebastian Coe said.
"He has gone way, way beyond athletics."
Now that the sport is suffering, still wounded by the Russian doping scandal and struggling to engage the next generation with compelling rivalries, he is walking away.
The void that remains is incalculable. Wayde van Niekerk is broadly identified as the pre-eminent talent following in Bolt's wake, but even he is struggling with the vast expectation that this casting creates.
After being vanquished by Ramil Guliyev over 200, the South African broke down in tears, having to be consoled for at least a minute before resuming his trackside interviews.
It was a reminder of Van Niekerk's status less as Bolt's logical heir than his polar opposite.
For all that the Jamaican is cocksure, swaggering, an inveterate party animal, the softly-spoken figure from Bloemfontein is intensely sensitive, offering many a glimpse of his vulnerability.
When Van Niekerk runs a full-throttle 400, he is so broken by the experience that he is often physically sick.
Bolt at his best, by contrast, was so at his ease with his gifts that the broke the 100m world record in Beijing despite dropping his hands and beating his chest several strides before the line.
Time can be a cruel and capricious mistress, though.
From his late Noughties pomp, Bolt has been slowing by almost imperceptible degrees for the best part of eight years.
Finally, here in London, his opponents have caught up with him.
A once effortlessly languid motion has begun to look laboured.
Painful as it might be, the time is surely right for him to bid farewell.
For he should exist in our minds as a supreme force, not an ageing champion chasing one last shot.
He bowed out last night in a relay, a discipline with which he has had a chequered relationship.
While he purports to love relays, regarding the task of anchoring Jamaica to glory as a signal honour, it is a former relay team-mate who has tainted the lustre of his otherwise immaculate Olympic canon.
But for Nesta Carter, who ran the opening leg at Beijing 2008, recording a positive 'B' sample for the banned stimulant methylhexanamin, Bolt would be facing retirement with an unparalleled 'treble-treble' of sprint titles at the Games.It is not a gripe, one senses, that will trouble him for long.
Much like the defeat by Gatlin that ended his individual career last Saturday, Bolt's loss of a nine-year-old gold medal as a consequence of a compatriot's misdemeanour is essentially a footnote to his feats.
His is a greatness beyond compare.
Nobody, not even him, knows quite what comes next. A few nightclub visits, perhaps.
All that is certain is that he is shutting down the kind of sporting electricity that might never be reproduced in our lifetimes.
Enriching, affirming, one-of-a-kind, Bolt can slip off into his sun-kissed retirement content.
For him and for all who watched him, it has been quite the ride.