Ulster's Paddy Jackson's omission from Ireland's match-day 23 for tomorrow afternoon's Aviva Stadium showdown with the mighty All Blacks comes down to the fact that he is a specialist number 10 rather than a Jack of all trades.
That was pretty much how coach Joe Schmidt chose to explain it when he announced his starters and replacements for the most daunting task in modern-day rugby – trying to upstage the world's best team on a day when they are hoping to create history by winning 14 out of 14 Tests in a calendar year.
Admitting that Jackson would have started had Jonny Sexton not recovered from the hamstring injury which forced him to withdraw at half-time against Australia a week ago, Schmidt said Leinster's Ian Madigan had been given a place on the bench once again by virtue of his ability to play in several back-line roles.
When he omitted Jackson and included Sexton for the Australian game, he included 22-year-old Luke Marshall at inside-centre. Then the explanation was that with Sexton at 10 and Brian O'Driscoll at 13, Marshall would have experienced minders left and right.
But although Sexton and O'Driscoll both play tomorrow, Marshall's place went to Gordon D'Arcy.
In addition to Sexton and O'Driscoll, full-back Rob Kearney has recovered from his calf injury and he too starts.
Schmidt said: "All three took full part in training (yesterday) and Rob trained well on Wednesday.
"Really it was just a case of getting them all on the training pitch together, confirming they could run and kick fully and, therefore, play."
Elaborating on his decision regarding Jackson, Schmidt offered the 21-year-old Ulsterman some timely words of encouragement.
"If Johnny didn't take the pitch then Paddy Jackson would have started at 10," he said. "We would have had confidence in Paddy, but we've got confidence in Johnny with the leadership qualities and that tips the balance."
And making the same point as had been the case when he unveiled his 23 to face the Wallabies, Schmidt repeated his logic, saying: "Again, it's coverage with Ian Madigan. If we get an injury to someone like D'Arcy it gives more flexibility.
"At this stage Paddy plays 10 and he doesn't play other positions."
Schmidt's choice of words – "at this stage" – may yet prove significant, though in view of Ulster's choices elsewhere it is not blindingly obvious where else the Ireland coach feels he could gain experience at provincial level. His next conversation with Ulster coach Mark Anscombe could be interesting.
"Gordon D'Arcy gives us the experience," Schmidt said in the course of explaining his thinking a little more fully. "Earlier in the week we weren't sure whether Johnny would make it, so it would have been important to have some experience around Paddy Jackson, and so that almost made that decision for us."
D'Arcy's selection – despite his indifferent form against Samoa in the opening Guinness Series Test two weeks – is harsh on Marshall, given that his two minders are in the team.
For future reference then, and with one eye on the bigger Six Nations Championship-shaped picture, the status quo is that in Sexton's absence, Jackson is his natural replacement. However, when Sexton plays, Madigan gets a seat on the bench.
Meanwhile the wisdom or otherwise of the selection to face the All Blacks will be revealed tomorrow. In the build-up to this game, with doubts over the fitness of Sexton (pictured), O'Driscoll and Kearney senior, it had been felt that if Ireland managed to get any two of that trio patched up sufficiently to enable inclusion, they would have done very well.
I am not aware of a single pundit who foresaw a situation in which all three would figure in the starting line-up; that one came right out of left midfield.
In the circumstances it can be only mean one of two things; either Ireland played a very cute game of cards during the week, or – more worryingly – they have gone for broke and are taking a huge risk in the hope that things work out better than anyone appeared to be anticipating this time last week. And 'anyone' in this instance includes Schmidt and Les Kiss.
Sexton had been told he had to train fully in yesterday's session if he was to be included. The 28-year-old Racing Metro player came through to the satisfaction of Schmidt, his former coach at Leinster, of course, where they built up such a strong working relationship, giving rise to a lot of mutual trust and respect.
O'Driscoll's recovery from a calf problem will see him equal Ronan O'Gara's record of 128 Ireland caps.
Kearney's rib injury has cleared, too, and he is joined in the back three by his young brother, Dave, who marked his international debut with a brace of tries in Ireland's 40-9 rout of Samoa. He takes over from Fergus McFadden who, like Marshall, is a faller following the defeat by Australia.
Immediately behind the pack, which is the same as that which started – and struggled – against those Wallabies, Conor Murray is restored at scrum-half, thereby renewing his partnership with 2013 Lions colleague Sexton.