Alan Quinlan: Jackson needs to be Sexton's rival, not just his understudy
Joe Schmidt made an interesting point after Ireland's defeat to New Zealand. Referencing the World Cup quarter-final against Argentina, when injury and suspension deprived him of five of his regular starting XV, Schmidt looked at the fact Johnny Sexton was likely to miss today's game against Australia as an opportunity rather than a disaster.
"Remember we were down bodies against Argentina (Paul O'Connell, Jared Payne, Sexton, Sean O'Brien and Peter O'Mahony) and it hurt us," Schmidt said. "So we have to be ready if that sort of thing happens again. One man out means another gets his chance."
So already, we can look through the window of the coach's mind. He isn't just thinking about today but also Japan in 2019. And while he's at it, he's thinking back to October 18, 2015, the day his plans to reach a World Cup semi-final came apart.
A year on, you can see how he has learned from the experience. Garry Ringrose, Joey Carbery, Ultan Dillane, CJ Stander and Josh van der Flier have all been capped for the first time. So have many others - but my point is this.
At last year's World Cup, those five players were below the radar. Now, you couldn't imagine an Ireland squad being picked without any of them in it.
And that's before we mention Robbie Henshaw, Paddy Jackson, Iain Henderson and Tadhg Furlong. That's nine players who are aged 26 or under, nine players who should feature for us in Japan three years from now.
Now it goes without saying that three years is a long time in rugby. This time in 2013, remember, we were denied a victory against the All Blacks when we had Brian O'Driscoll and Paul O'Connell in our team. Three years ago, Cian Healy was the No 1 loosehead in the world. Now he is not even No 1 with Leinster - although he is still a class act.
And Healy is the perfect example of where we're heading. He and Jack McGrath provide world-class options for Schmidt at loosehead. Rory Best and Sean Cronin offer depth at hooker, while Furlong and Finlay Bealham have contributed to solve what was once a problem position for us at tighthead.
In the second-row, Schmidt has a choice between two men who will be stars - Henderson and Dillane - and a couple of old dogs for the hard road in Devin Toner and Donnacha Ryan, both of whom have been exceptional this month.
And we haven't even got to the back-row yet: Jamie Heaslip, Sean O'Brien, Stander, Van der Flier and O'Mahony are established as world class operators.
Jack O'Donoghue has the potential to join them, while the luckless Jordi Murphy was having a stormer in Chicago before his injury.
While the cover for scrum-half Conor Murray is a worry, the back-up to Sexton no longer is. A year ago, the gap between Johnny and his understudies was frighteningly large. And then South Africa happened.
Paddy Jackson seized his chance. And while South Africa's subsequent meltdown has slightly diluted the quality of that Irish victory, we cannot take away from the mentality Jackson showed in the first half of that game in Newlands, when he was targeted by the Springboks.
Today, he's offered another chance to show that not only is he capable of standing in for Sexton but more significantly that he's an asset who, over the course of time, could be upgraded permanently from the bench to the starting XV.
This is the sort of crossroads game that happens right across sport when big players are missing. Offered a chance, a guy can make a massive step forward as a person as well as a player. If South Africa was Jackson's coming-of-age moment then today is the time when he can actually say, 'I'm more than just a stand-in. Start comparing my game to Johnny's and see who is better.'
You need that kind of confidence from your out-half. Sexton provides it, offering composure and control, as well as an air of assurance to the team. No side wants their No 10 slicing kicks into touch or looking nervy. They want a guy who is in command, who makes the right decisions - knowing when to run, when to kick.
Can Jackson do that against the Wallabies? There is no reason to doubt it.
Nor is there any call to doubt Carbery, who we knew next to nothing about as recently as August but who we have subsequently seen as this incredible talent - the possessor of outrageous skills, who runs threateningly with the ball, who has a wicked sidestep, and whose physical attributes appear to be matched by a strong mentality. Coming on against the All Blacks was a challenge. He stood up to it.
Now to Ringrose. Would we have been able to compete 12 months ago had we lost Sexton and Henshaw in the opening half of a game against the All Blacks? No. But last week we did. Ringrose, on his second Test appearance, in an unfamiliar position of No 12, stood tall.
You can't help but be excited by how these experiences will stand to him ahead of the World Cup in Japan.
Think about where Toner was in 2013 and how he has matured in the intervening years and now consider the advantages this early exposure to big-match atmospheres will be to Ringrose, Carbery, Jackson, Van der Flier and Furlong.
By 2019, these guys may even be superstars in world - not just Irish - rugby. At the very least they are coming into an environment where the expectation is to win, and where the quality of the coaching they are getting, not just from Schmidt but also from Andy Farrell, is incredibly high.
Between them, their shrewd investment in players is already bearing fruit. We have every reason to be excited about the years ahead.
Today then is a fine test of where we stand. The Australians are on a rebuilding process of their own.
And they are also on leg four of a five-game Grand Slam. Last weekend, they rested half their team against France and still won.
So while today's game may seem a little like the day following the Lord Mayor's show, this remains a massive match between sides ranked third and fourth in the world.
I certainly wouldn't be underestimating the Wallabies, who have undergone a lot of transition in the last 12 months, losing Matt Giteau, Drew Mitchell, Adam Ashley Cooper et al.
"Sometimes you need short-term pain for long-term gain," Michael Cheika said, by way of explanation for why he is exposing younger guys to Test rugby. You sense he likes to see character as well as skill in his men.
The same, of course, can be said of Schmidt. And today we'll see what Jackson, Ringrose and Henderson are made of. A test match in November 2016 is, in a way, the mocks before the real exam in Japan three years from now. Let's see if they pass.