Dan Sheehan's potentially serious knee injury in Saturday's first Test against South Africa is a reminder of just how cruel sport can be.
It was a completely innocuous incident that left the Ireland hooker with what is suspected to be a ruptured ACL, a routine tackle on South Africa's Eben Etzebeth where Sheehan jarred his left knee.
Sheehan's loss will have been felt right around the squad. The 25-year-old is only two-and-a-half years into his Test career, and 27 caps deep, but it's been a meteoric rise for the Leinster hooker, who would likely have been a first choice selection in a British and Irish Lions side, had it been picked on current form.
The cruelty is compounded with how quickly sport has to move on. There will be no time to dwell on his loss, or indeed that of Craig Casey, who is also ruled out of this week's second Test due to concussion. Dave Heffernan and Nathan Doak are now the squad, who are already deep into their preparations for this Saturday's game in Durban.
Rónan Kelleher knows the score. The Leinster man is likely to be promoted to the starting team in Sheehan's absence this weekend.
Two years ago, his own struggles with injury opened the door for Sheehan to cement his place as first choice for both province and country.
The 26-year-old (above) will now have a chance to impress head coach Andy Farrell against the Springboks at King's Park, and barring injury also through the Autumn Internationals.
But while he says he's ready to step up for Ireland, he's aware that it's come at great cost.
"I wouldn't say bittersweet at all," Kelleher says of the prospect of a start this weekend. "It's just bitter. You never want to see a team-mate injured, hurt or anything like that.
"It's unfortunate but that's sport. We'll deal with it as a group and move on quickly.
"He'll be a big loss [Sheehan]. There's competition in the squad, we just need to do our job, make sure put our best foot forward and leave the team in a good place."
Kelleher replaced Sheehan at half time in Saturday's first Test, and found himself as the central character in the game's big moment.
It was his turnover at a breakdown that won possession back for Ireland, leading to a James Lowe try on 57 minutes, but the score was chalked off by referee Luke Pearce and TMO Ben Whitehouse, after he was deemed to have rolled the ball back while off his feet.
Earlier this week, former Test referee Jaco Peyper, who is now part of the South Africa backroom team, said the officials had no option other than to disallow the score, although he conceded that Ireland may have a legitimate grievance over how Kelleher had been neck-rolled to the ground at the ruck.
There has been criticism over the TMO intervention for a technical ruck offence, rather than for foul play or a knock-on, although Kelleher concedes that by the letter of the law he did play the ball on the ground.
"It's tough in the heat of the moment. I went in to try and hook the ball backwards, it's fine margins in Test matches that decide things and unfortunately we came out the wrong side of it.
"I'm on the ground, trying to hook it.
"I suppose I was [surprised], but when you break it down frame by frame you can see I'm on the ground, so by the letter of the law.... [pause] but, yeah, at the time I thought I was on my feet, trying to get up through the ruck and trying to hook it back.
"Just, unfortunately, I hit the deck. But, yeah, I didn't know at the time I was on the ground playing it," he added.
Kelleher is set to make his 30th appearance of the campaign this weekend, which matches his tally from the last two seasons combined, after a series of injuries - most notably to his hamstring and shoulder - stunted his progress.
For some, a 30-game season would feel like a hard slog, but the 32-cap Ireland international says he's been loving a consistent run of rugby.
"I'm feeling good. I had a couple of injury-riddled years really and I'm just happy to get a good string of games together.
"The body feels a lot better for it, it's probably one of those things where you build resilience through playing and I managed to get a lot of that done this year which I'm pretty pleased with.
"It wasn't really affecting me really [confidence-wise]. After you get injured, you're thinking about it and it's disappointing. When you think about it, you only get three games to start off a year and you're out again to January or something like that.
"It's more frustrating when you're looking back on it. When you're in the moment, you're not really thinking about that, you're just focusing on playing and trying your best to play well and implement the game's team plan."
In each of the last two meetings between the sides, South Africa have disrupted the Irish lineout to great effect.
In the World Cup meeting last year, Ireland lost all four of their opening lineouts on Kelleher's throw, while the hooker had a 66.6% retention off nine throws in his 40-minutes last weekend.
"They've a very good lineout defence, they're very tall second and back-rows who get up in the air.
"It's just about honing on our drill, our calling voice and making sure we're on the same wavelength really.
"It's about committing to the throw, to the lineout drill as well.
"We believe if we get all of our stuff right we'll come away with the ball. Committing 100%, making sure of everything; top of the jump, top of the lift and nailing those little details."
"We put the menu together throughout the week, a lot of it comes from analysis from previous games, we put it together and go in with a clear plan about how we're going to attack our lineout defence," he said of Ireland's lineout strategy.
Kelleher started the World Cup meeting between the sides last September, and set the tone for a monumentally physical encounter when he put in a dominant tackle on Damian Willemse in the opening minute of that game in Paris.
And if he's named in Farrell's line-up, which will be confirmed on Thursday afternoon, the hooker says Ireland will have to reach those heights if they're to level the series.
"There's obviously a lot of chat around their physicality and what they can bring, and I suppose it's a really exciting challenge to try and one-up them physically, is the way I'd put it.
"It's a massive challenge that I know everyone in the team looks forward to when you play a team like this, and you want to set down a marker and pitch up physically."
Listen to live commentary of South Africa v Ireland (4pm) on Saturday Sport on RTÉ Radio 1, and follow a live blog on rte.ie/sport and the RTÉ News app.
