In August, Bangladesh walked into Darwin, were bowled out for 54 in a warm-up match and then did something that only a few days ago sounded close to impossible: they beat a full-strength Australia by nine wickets in a Test.

It was the first Test victory by Bangladesh on Australian soil and only their second win over Australia in the longest form of the game anywhere. Not only that, but the result was a sporting shock that briefly made the rest of the world feel like it belonged to the winning side.

The online reaction said as much. People who barely followed Bangladesh were celebrating as if they had a personal stake in the result. Timelines filled with disbelief, joy and variations of the same question: how did that just happen?

That is the strange power of an upset. In cricket too, perhaps more than in most sports, an unlikely victory can become a memory that lasts a lifetime.

Cricket made for the unexpected

Cricket has always had a recipe for giant-killing.

Test matches are drawn out over five days, where conditions can change from one session to the next, pitches can deteriorate, swing can develop, and morning clouds can turn benign tracks difficult for batters. Any team that looks like it might have been out of contention on day one can still produce a fight for the ages 48 hours later.

It provides the smaller team with an opportunity, and an opportunity for the stronger team to prove its mettle, and, over five days, there is a chance for both to recover from a mistake. It's those opportunities that make for great upsets.

Great upsets in cricket aren't that common, but they're frequent enough to keep people hoping, and rare enough to keep people talking.

Bangladesh didn't merely survive in Darwin and wait for Australia to self-destruct, as they did in Hobart in the group stages. They bowled Australia out for 198 on the opening day, followed it up with a patient 426, and then refused to concede the victory, despite Cameron Green's century in their second innings, which was ultimately in vain.

They played a team with four seamers who each had more than 300 wickets on board.

That is, perhaps, the most important part of an upset: the context in which it comes.

Why giant-killing feels so good

It may have to do with something called reward prediction error, a hypothesis put forth by Wolfram Schultz, which holds that the brain generates a far stronger reward for something that was unexpected than something that was anticipated.

In other words, you feel a stronger thrill for an upset than a victory that was always on the cards.

Sports have long understood the value of an upset, and capitalized on it.

Few people talk about the many wins Australia has racked up against minnows like Bangladesh and Zimbabwe. But ask any cricket fan about the 2011 World Cup match where Ireland took on England and chased down 328 with Kevin O'Brien hitting 113 off 63 balls, and most will be able to tell you about it.

What made it special was the improbability of it. An eleven-wicket lead turned certain victory into a thrilling chase.

Had Ireland made the target look easy, it would have been a fine win, but something special happened when it seemed as if nothing could stop them.

Unlikely upsets always feel like they're part of a larger statement, even if they aren't. Even if no one talks about them the way they do about that 2011 game, upsets feel like a statement.

How giant-killing makes cricket history

Cricket has a long memory. Its history is etched in statistics, and in the fans' hearts and minds. An upset will always live on, long after the initial shock wears off, as a part of folklore. Take Zimbabwe's astonishing win over Australia in the 1983 World Cup, or Kenya's rise to the semi-finals in 2003, or Eire's win over England in 2011, or Afghanistan's path to the Test arena, and you'll see that they all have one thing in common: they made people think about non-Test-playing nations in a completely different light.

It is, perhaps, the only way these upsets leave a longer-lasting legacy.

It wasn't enough for Ireland to beat England once. It led to a conversation about associate nations and the need for an expanded World Cup, which, in turn, led to the format being changed so as to include more associate nations, and led to Eire, and other nations like Zimbabwe and Bangladesh, getting Test status in 2017.

A giant killing rarely creates an immediate impact on a nation's rise in the cricketing world. But it will always shape the way that people talk about them in the years to come, making it easier to get past that initial step of beating the big teams.

Bangladesh, perhaps, can do the same now, after their win over Australia. Australia drew the series in Mackay, after bowling Bangladesh out for 64, and 95, and winning inside two days. One giant-killing might not be enough to propel Bangladesh into the upper echelon of Test-playing nations, but it will make the next upset much easier to happen.

Why fans love backing the impossible

There is something undeniably romantic about backing the underdog.

Most sports fans know their team will lose occasionally. For some supporters, it will be more than that. But they return, again and again, to the grounds to buy a ticket. Especially in cricket.

A county match on a cold Friday morning in April does not promise the excitement of a spectacular afternoon. A domestic fixture can pass by without the outside world knowing. But in a county match there is always the possibility that something will happen.

The possibility that a teenager will declare himself or a part-time spinner will take five wickets, or a team chasing down an impossible score will touch the winning run or that a player nobody thought they would see play the game they will remember forever.

The attraction is not in certainty. It is in possibility.

That same feeling is carried through into the international arena, where an outsider is up against a juggernaut, and fans, who have no particular link to either, suddenly find themselves wanting to see the underdog reach their goal. To experience what life is like if the impossible became a reality.

It is what made Bangladesh's win in Darwin so special and why Mominul Haque's final runs at Marrara Oval were not just a cricketing achievement, but one that connected to a disparate group of fans.

A small minority of the crowd in green and red, from the Bangladeshi supporters' group, provided the noise inside the ground. But much of the celebration was seen playing out online, where many of the people who watched the match, and certainly those who had not seen it, were expressing their delight at the result.

It is the peculiar social currency of an upset that, for a handful of hours, the boundaries between fanbases disappear. You do not have to be a supporter of Bangladesh to enjoy Bangladesh's win over Australia. You only need to appreciate the possibility of something the sport might produce that no one predicted.

The matches we remember. The greatest compliment an upset can receive is also the simplest: people remember where they were.

Ask an Irish supporter about Bengaluru in 2011 and you are likely to hear about the pub, the sofa, the radio or the people around them. Ask a Bangladeshi supporter about Darwin and the answer will be just as personal.

That is why cricket's greatest upsets matter. They are not simply victories in an archive. They become reference points. Things which fans return to, stories passed between generations and proof that, however strong the favourite, the result has not yet been decided.

Cricket's underdogs do more than win matches. They remind everyone why we keep watching.