Sport is a cruel business.
At Beijing 2008, Shanaze Reade went into the inaugural Olympic BMX competition as a white-hot favourite.
The 19-year-old trailed her French rival Anne-Caroline Chausson in the final, attempted a risky overtaking manoeuvre and fell.
Four years she waited to put that wrong right. She was no longer the favourite for gold, but her semi-final times showed medal-winning pace.
Her starts in all three heats impressed particularly - propelling her ahead of the pack and away from trouble.
Then the final - her moment of redemption. The barrier dropped, and something strange happened.
Instead of surging clear, Reade hesitated fatally. She found herself to the rear of the pack, and by the time she got up to speed it was already too late.
Sixth place. No medal.
Did the occasion get to her, did she freeze up? Or was it a simple case of bad timing?
See you in Rio in 2016.
Then came Liam Phillips - much less fancied but an impressive qualifier for the men's final.
This time the Briton got a flier, leading into the first corner, Could this be the moment for Britain?
But Phillips's foot slipped off the pedal and he lost momentum, before eventually falling as he tried desperately to recover.
A cruel business, but the tiny margins are what make sport interesting.
One person's tragedy is another triumph, and you could hardly begrudge Colombia and Latvia their first gold medals of the games, courtesy of Mariana Pajon and Maris Strombergs.
In a Games of so much British joy, it was strange to feel deflation. But without the despair there would be no elation in victory. Not that it will make Reade or Phillips feel any better.
Nonetheless, this was a triumphant day for BMX in front of 6,000 whooping fans at a gleaming track.
BMX plays up to its youth credentials, with a DJ scratching furiously away at his turntables, and stunt bikers in the intermissions. Despite the X-Games facade, it has everything you could want from an Olympic event.
Not only does it provide drama, entertainment and (most of all) crashes in abundance - it is clearly a serious sport.
Reade trains in Manchester with the rest of the British track cycling team - she is a formidable athlete.
This is no hobby, it is a sport with global participation and a dedicated following.
While the Olympic Games uncomfortably shoehorns the likes of golf and rugby sevens into its schedule, BMX is an example of the kind of thing that really belongs here.
BMX ARENA - VENUE SCOREBOARD
ACCESSIBILITY/FACILITIES: 7/10 - It has a slightly odd position, squeezed between the Velodrome and the Basketball Arena virtually out of sight. The stadium itself is great, though.
VIEW: 8/10 - The track snakes back and forth in a series of hairpins, giving everybody a good view of virtually everything - and from the top of the stands you get rather a nice panorama of East London. However, the stands are a little further from the track than they might be.
FANS: 8/10 - A phenomenal turnout for the British riders was complemented by large pockets of support from Latvia, Colombia, France, Australia and the Netherlands. The fans were whipped into a near-frenzy, but the air disappeared from the stadium after the finals.
SPECTACLE: 9/10 - BMX is rated the most dangerous sport at the Olympics, and Brazil's Squel Stein was stretchered off after a huge fall in the semi-finals. Human nature being what it is, the crashes add to a spectacle full of thrills - though light on tactical intricacies.
X-FACTOR: 9/10 - A packed press area and the presence of David Beckham and desperate cool-hunters David Cameron and George Osborne tells you this certainly has something. It doesn't necessarily feel like the Olympics, but it is extremely enjoyable.
TOTAL SCORE: 41/50
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Alex Chick will be writing from London 2012 throughout the Olympic Games.