It doesn't happen so often but when it does you are left with the most undemanding duty. It is to keep what you have seen very close for the rest of your days. That was the obligation Kauto Star and his jockey, Ruby Walsh, imposed on all those who saw them make history here yesterday.
History? It was the least of it, the history.
Kauto Star became the first fallen champion of the greatest jump race of them all to come back and reclaim the Gold Cup, but when the hats went into the air and the valley was filled with rolls of thunder from the great crowd and complete strangers found themselves hugging each other it was not because of what the past had brought to the present.
It was about something a lot less reflective than that. It was, almost entirely, about the wonderful union of a great horse and a great jockey, something once described by a leading trainer as a mystery known only to the horse and the jockey – and God.
Yesterday, like the rest of us, God was surely consigned to the role of another spectator filled with awe at the perfection of Kauto's stride and Walsh's feel for every nuance of the challenge in front of his former champion.
When the nine-year-old French-bred, Somerset-trained national hero lost his crown to his spirit-crushing stablemate Denman last year, it was as though a terrible fault line in his otherwise brilliant talent had been exposed for all time. He jumped raggedly and exhaustingly and had nothing left when Denman pushed for home. It could not have been a greater contrast yesterday when Denman, who could only confirm his bravery – and the suspicion that last year's effort had inflicted lasting damage – was left trailing when they hit the cruelly rising ground.
Kauto Star unfurled all his beautiful, natural running rhythm once again, but this time there was something else, something that made the hearts of all his admirers, and especially his backers, race with anticipation after just a couple of the 22 obstacles.
He was jumping so flawlessly, gliding with such little difficulty over the fences, that one enraptured admirer exclaimed he was flying like Pegasus. A more knowing eye, though, made an instant correction. No, it was like water going over the pebbles.
Kauto Star, indeed, was moving like a powerful stream and it was only at the last two fences, when Walsh reminded him that it was time to come home, that you got a better sense of his superbly marshalled power. The rhythm was still there but now you could see the contours of effort as the winner stretched out before Walsh first punched the air, then made, with great deliberation, the sign of V-for-victory.
Denman was beaten by 13 lengths, but if that sounds like a slaughter it does nothing to define the way the beaten champion so gamely battled a rival who, on this occasion, had been perfectly prepared – and, perhaps as never before – sublimely handled.
Walsh had enjoyed the Cheltenham of his or any other riders' life, delivering a 20-1 winner, American Trilogy, in the second race to smash the record of six wins for the Festival, before he mounted Kauto, but the fact that he was plainly on fire, riding with a touch and an acutely honed instinct for the pace of every race, was still no adequate preparation for the mastery which was to follow.
Later, and with that generosity which tends automatically to accompany the courage and the hair-trigger judgement of the most successful of the National Hunt riders, Walsh made it sound as though he had been doing not so much more than hacking around a Kildare meadow.
He declared: "It's a privilege to ride a horse like that – he'd be the horse in a million for any jockey. For the first circuit I was just trying to get him switched off, which he did and I knew early on he was going well and better than last year.
"He jumped the fourth-last and the third-last brilliantly. We were always travelling and after he hit the third-last running, I knew we were in business. I went a bit early – but it didn't matter. He's a wonderful horse."
But then Walsh's own stock, riding so high in the company of his trainer Paul Nicholls, who would have reproduced his feat of last year in saddling the first three but for the intervention of third-placed Exotic Dancer, means that he is now keeping the easiest company with Kauto Star. "A perfect ride," said Nicholls, whose consolation at conceding a top-three position surely came in the fact that the men responsible were two of the greatest names in the business, Jonjo O'Neill, trainer, and Tony McCoy, jockey of the ages. When O'Neill the jockey won one of the most dramatic Gold Cups on Dawn Run in 1986, overwhelming Wayward Lad after trailing him at the last, some declared they would never see a more thrilling race. Yet if the margin of win and loss was so much greater for Kauto Star and Denman, 13 lengths against the three-quarters of a length advantage of Dawn Run, what we saw yesterday was undoubtedly a rival spectacle to set before the Queen. Her Majesty may have been disappointed by the seventh place of her Barbers Shop, but she cannot have regretted her pilgrimage.
She didn't get to see a dogfight of a finish, but then you can see one of those at Wincanton or Towcester any old day.
At Cheltenham we saw something else. We saw one great champion regain his ground, magnetically and historically, and another one surrender his own only after a run of quite moving courage.
Ruby Walsh said he was privileged. So, too, was the Queen – and all her subjects.