The temperature of the week has to be just right in the lead-in, the dressing-room calm, composed and knowing, the players working in union with the game-plan laid down.
The late decision to leave Brian O'Driscoll on the bench and the non-selection of forwards Richardt Strauss and Kevin McLaughlin must have come as a blow.
At least the old back three of Rob Kearney, Isa Nacewa and Luke Fitzgerald are in harness, even though none is 100pc match-sharp, with the versatile Fergus McFadden moving into the midfield to partner Gordon D'Arcy.
This is a process that Leinster have mastered in the last five seasons, starting with Michael Cheika, continuing with Joe Schmidt.
It has been good enough to seal three European Cups in four years. It can be good enough to give Leinster a shot at a saving day at Exeter Chiefs.
"Inevitably, there is a lot of hype. There hasn't been as much hype about the particular situation we are in, in my time, because we haven't been here before," said Schmidt.
Hype can turn to hysteria if the right foundations are not in place. The thread of experience running through Leinster makes any occasion, no matter how tall, one that serves to motivate rather than intimidate them.
"It is not a comfortable position to be in. I would much rather be in control of our own destiny. We've looked at the permutations. We can't control those. All we can do is make sure our performance is as good as it can be.
"We are very much process- and performance-driven to try to get the performance that will give us the win. In the end, we've got to get the four points, first and foremost."
Schmidt was playing down the necessity for Leinster to rack up the four tries that are paramount to their cause. This does not hide the fact that they need them badly, very badly.
"If enough teams muck up, four points might be enough. That is highly unlikely. But if we end up getting nine points from the next two games that could even be sufficient."
That being said, there is a hell of a better chance securing five from The Scarlets at home than Exeter Chiefs away at Sandy Park, where no English Premiership club has been able to hit them for four.
In addition, coach Simon Easterby has left centre Jonathan Davies and hooker Matthew Rees as replacements with George North unable to return from a neck injury. They look ripe for picking off.
There is nothing to rev the engine, or the voice, of the home support like an early kick to the corner, going for seven when three are on offer. Expect to see Jonathan Sexton go for gold.
Regrets? Schmidt has a few. Not too few to mention: "We were in that game in Clermont. We feel we probably had a couple of opportunities to steal the win or at least the draw. Not getting that is a regret.
"Not having as much firepower as we would have liked to have had -- that's a regret."
Schmidt is not a one-eyed coach. He reached back into his crystal clear memory to remind the listening press on Thursday that Exeter Chiefs let Leinster off the hook in round one.
"There have been positives as well. I don't regret that (Ignacio) Mieres lost his compass slightly with his last kick. You always feel that there is a little bit of stuff that has gone your way and a little bit that hasn't."
There has always been the threat that, sooner or later, Clermont Auvergne would come out on top of their almost annual jousts with Leinster, especially when they add to their firepower every season and Leinster have been so weakened this term.
Schmidt only had to crane his neck and look north to see how The Scarlets can be controlled and, ultimately, crushed, as they were by Ulster in the PRO12 at Ravenhill last Friday night.
"I thought Ulster did a good job to build scoreboard pressure. They didn't play any different than they normally play and scored a number of tries late in the game.
"If you can build scoreboard pressure, you tend to force the other team to open up the way they are playing. Maybe that's the way to force the result."
There is a clear instruction from the coach that the players have to think on their feet. They have to sense when the time is right to go for the jugular.
"Sometimes if you try to chase the game from the start, that scoreboard pressure can be against you. It allows your opponent to play conservatively because they know you are chasing the game.
"They can push more guys forward in their defensive line, not cover as much in the back field because you're not going there. To chase a game when it is nil-all is a dangerous circumstance.
"We might say, 'Look, we've built scoreboard pressure, let's try to chase the game a little bit more.' That is something we might do, especially in the second half, if we feel that we have a buffer on the scoreboard.
"We just focus on getting the buffer first, focus on building scoreboard pressure, because if we can do that, then not only are we prepared to open the game up, they are effectively forced to open the game up."
Leinster: R Kearney; I Nacewa, F McFadden, G D'Arcy, L Fitzgerald; J Sexton, I Boss; C Healy, S Cronin, M Ross, L Cullen (capt), D Toner, S O'Brien, S Jennings, J Heaslip.
The Scarlets: L Williams; A Fenby, G Maule, S Williams, K Phillips; A Thomas, T Knoyle; P John, K Owens, J Adriaanse, G Earle, R Kelly, R McCusker (capt), J Turnbull, K Murphy.