Ireland must be ready when opportunity knocks - O'Brien
We presume Joe Schmidt opts not to take the commentary feed when he reviews the footage of Ireland games, but if he did the despairing words of Jonathan Davies would haunt his dreams.
"They've got to go wide now, they're short!" the former Wales out-half screamed as Ireland ran into a red wall for 45 phases in Cardiff last March. Ten minutes later, he roared "Gotta come right, gotta come right, Ireland - they've got numbers!" while Jared Payne and Tommy Bowe waved their hands in the air hoping their team-mates inside could see the space in front of them.
On both occasions during that epic second half as Wales held out, Ireland couldn't see the space and exploit the opportunity in front of them and the Grand Slam slipped from their grasp.
A week later, they beat Scotland to claim the title, but when they returned to Cardiff in October to face Argentina they again left chances out on the pitch as they exited the World Cup.
The big question this week is whether the Six Nations champions have learned their lesson.
"We have in certain games, but it can always be improved on," Sean O'Brien said. "We are creating those opportunities so we can take a lot of confidence from them and just make sure we try to finish as best as we can.
"Another big thing for us over the past few years against Wales has been our discipline. That can be tightened up a lot and it will add to creating a few more opportunities for us.
"They defended very well (last year) but we had opportunities at certain times in their '22 and we didn't finish and that kept giving them air to breathe, but in fairness to them that day they defended very well. But we didn't look back any further than the Argentina game, we're trying to move forward the best we can.
"Against Argentina, we created a lot of opportunities and that's what people forget, we had chances to score at crucial times and we didn't.
"We can take a positive from that and just try and finish off those opportunities when they come, you don't get as many at international level and when you do you have to take them. Looking back on that day, it was more about the opportunities we left behind than anything the Argies did."
Since Argentina, Ireland have been stripped of a host of impact players like Paul O'Connell, Iain Henderson, Cian Healy and Peter O'Mahony, prompting fears that they could be bullied up front by a sizeable Wales XV on Sunday.
The loss of so many ball-carriers could prompt a re-think from Schmidt who has emphasised Wales' size in his public utterances to date.
"I don't think so," O'Brien said of the idea of change. "The players that are involved in this group are in the same position as the lads. They have skill. We have players who can play in different positions. Nothing changes. It is about doing our jobs and doing it to the best of our ability."
The task that awaits O'Brien is a familiar one. Wales are expected to field their regular back-row trio of Dan Lydiate, Sam Warburton and Taulupe Faletau who will combine for their 29th Test in Sunday's game.
O'Brien has faced them as a combination twice, while he toured Australia with the three of them on Lions duty three years ago and, having served under Warren Gatland on that tour, he knows what to expect. "The first thing they bring is that huge physicality," he said. "We always expect that from them through the years. They've a lot of attributes to their game. They have a good kicking game. They're good in the air. They've a big pack. They've a great back-row.
"They've a lot of strings to their bow. The physicality one is one which they pride themselves on. It sets the tone for them. They've been playing together a long time now. Any of the back-rowers that they play are world-class players. We always know it's going to be a tough day at the office around the breakdown.
"They're hugely physical as well, throughout their whole pack - especially in their back-row. It's a nice challenge for us and one we're looking forward to.
"They know us pretty well and we know them. It'll be fairly similar fare come the weekend of what way they want to stop us and we want to stop them. It'll be a tough battle out there."
So, what is the key to getting on top against them?
"It's about implementing our game plan as well as we can and as accurately as we can and putting them under pressure," O'Brien said.
"Hopefully we can ease the pressure on ourselves, they'll come with a lot of aggression and physicality as they always do but I think it'll just be a cracker of a game and it'll add to it because we know each other so well."
Over in Wales, they are considering starting Liam Williams and Lydiate despite a lack of recent game-time as they continue to try and shift the favourites' tag on to Ireland's shoulders. "It's hard to be the underdog when you've been champions for the last two years," centre Jon Davies said. "I think that tag goes to us."