A long jumper overstepping by an inch, a swimmer reaching for the wall a fraction too soon, a sprinter betrayed by nothing more than a twitch; all that back-breaking work, all those sacrifices, all that emotional baggage, up in smoke - rendered pointless - in an Olympic second.
But those are the lucky ones, for at least they made it. At least they can say they were there.
To witness real desolation - and its attendant glory - get yourselves down York Hall in London's East End this Friday and Saturday: two young men putting years of themselves on the line, fighting for the chance to represent Great Britain at the London Olympics. Forget about the earthiness of the venue, you could argue it is bigger than the Olympics itself.
For Birmingham's Khalid Yafai and Andrew Selby of Barry, this wasn't how it was supposed to be.
Pitched into a best-of-three 'box-off' for the squad's flyweight berth, both men have every right to think they are better than this. But this is the perverse price of success. Where once Great Britain had to be content with one or two-man teams and the odd medal here and there, head coach Robert McCracken has inadvertently created a house of heartache and pain.
"I've put everything into it," says 22-year-old Yafai, who competed at the 2008 Olympics in Beijing. "I've been here since I was 17 years old, having to get the train up every week, all the training, having to miss out on the things my friends do at home, my family. It's pretty hard, but it's all part of the dream."
Selby, also 22, says: "This [box-off] is bigger than actually being at the Olympics, because if I lose, I won't be representing my country in London. This is what I've been waiting for all my life, this is why I became a boxer. It's hard to explain, but I want it more than anything."
Selby admits that being involved in the box-off is "a bit of a downer" and claims he is more deserving of an Olympic place than his rival. And he has a pretty strong argument. His has been a wildly successful year, in which he has won gold at the European Championships and silver at last month's World Championships in Azerbaijan.
In the World Championships final, Selby lost by a single point - had he won, he would have automatically qualified for the Olympics. As it was, the fact that Yafai also made it as far as the quarter-finals meant an effective tie-break was required, constituting two fights at the GB Championships this weekend and a possible decider at the Olympic test event later this month.
For Yafai, watching Selby compete in that final in Baku was sweet torture. "My hands were sweating, I was twitching like nobody," says Yafai, who won European silver in 2010 but, as Selby is keen to point out, is without a medal at major championships this year.
"I definitely wanted him to lose. I'd be lying if I said I wanted him to win. I would never normally wish defeat on any of my team-mates - but on that occasion I did, and I don't think anyone would blame me for that. I have no sympathy [for him] whatsoever, because if he had won, he would have destroyed my Olympic dream."
Yafai arrived for training at Sheffield's English Institute of Sport on Tuesday just as Selby was finishing up - two thrusting tigers meeting fleetingly in a jungle clearing, sniffing the air for signs of weakness, before melting from each other's sights and readying themselves for the day of reckoning, when supremacy will finally be decided.
"We're keeping out of each other's way, being kept apart," says Selby. "We don't speak at the moment, but that's just part of the game. No-one's said anything, but some people might want him to win, some people might want me to win. But we'll be friends after the fights."
Yafai admits: "People haven't been open about it, but you just know [they think Selby will win]. Almost everyone has written me off - people outside of the camp and in the camp. But I'm ready to show what I'm capable of, I've got a really good feeling about this.
"If he loses to me this weekend, everything he's achieved this year means nothing. Nothing we've achieved this year means anything. But I don't think about losing."
Adds Selby: "I don't want to think about losing, either. But yeah, I have thought about winning - and it's a really good thing to think about."