Leinster became European champions for the first time in 2009.
They cemented their champion spirit in 2011 when coming back from the dead in The Miracle Final against Northampton Saints.
You can accept miracles happen all you like. It is not until you witness one at first-hand that you can truly believe.
The fabric of Leinster, like Munster, is that they believe because they have been there, unlike Ulster.
The Northern Province has yet to have that light-bulb moment in Europe.
They can bully and blast clubs at Ravenhill. It is when the foot is pressed against the throat at places like Leicester that they can come up short of the points.
But they are not too far away.
The way Leinster, Ulster and Munster came on strong in the final quarter of their respective European Champions Cup matches was a compliment to the strength and conditioning coaches at th e provinces, the IRFU's Player Welfare Programme and, most importantly, the inbuilt mindset.
"We're always in the fight. Always," said Leinster captain Jamie Heaslip.
"I don't know if a lot of you guys (media) realise over the last several years, a lot of our scores have come in the last 20 minutes. We always back ourselves. Always.
"Even if we're fifteen points behind going into the last ten minutes, I'm always optimistic. If we back our drill and execute our drill I always think we can score, be it three points, five points, seven points, whatever it is".
Leinster and Munster did what they have learned to do. Ian Keatley's drop goal at Sale was reminiscent of Ronan O'Gara's against Northampton in the Autumn of 2011.
By now, it must be in the DNA.
Leinster were almost made to walk the plank that was The Millennium Stadium by The Saints in the 2011 final. That which did not kill them made them stronger.
On Sunday last, Leinster were in free-fall at 20-8 with a shredded side, denuded of so many big names, but replaced by so many embedded in the same culture.
"We've played in some pretty big games and come back from some pretty big deficits. That's nice to know. It's in the bank.
"But I don't like testing that theory always, to be honest," continued Heaslip.
Jack McGrath was stupendous. Dominic Ryan and Rhys Ruddock worked their socks off. Noel Reid grew into it. Darragh Fanning is showing the real benefit of consistent game time.
"The composure to fight your way back and keep going back to drill and process and build that intensity was really pleasing.
"To be running down the hill at home with everyone on their feet was really positive," added coach Matt O'Connor.
"Success gives guys belief. It gives them somewhere to go when things are tough. We weren't being outplayed. We weren't being outplayed.
"It gives them the confidence to keep doing the things we do in training. We didn't go off script. We didn't chase the game. We just kept doing what we do".
Leinster might have to go to the well again at Castres Olympique on Sunday.
It was only nine months ago that they slumped behind by fourteen points early on before their championship mettle and superior conditioning wore down the French club 29-22 at Stade Pierre Antoine in January.
O'Connor was there with them. He knows what to expect: "You don't want to get ambushed.
"We probably let ourselves down the first twenty minutes of the game down there last year. We went down 14-0 really early in the game. We've got to make sure that we manage those minutes.
"They will be very hungry, I think, to kick start their season against Leinster and they will be looking at that as a building block for the Top-14. We're going to have to make sure we're very good".
He also knows he won't have Dave Kearney, Brian O'Driscoll, Kevin McLaughlin and Jordi Murphy. Probably not Luke Fitzgerald.
There was also significant impact off the bench from Cian Healy, Marty Moore, Leo Cullen and Shane Jennings.
None will be there.
What he will have, however, are Richardt Strauss, Kane Douglas, Rhys Ruddock, Dominic Ryan, Noel Reid and Darragh Fanning all gunning for game time.
If Leinster can come away from Castres with four points and emerge from Pool Two, the long-term benefits for the club will come flooding in.
The experienced banked by the men in place and the confidence they gather will make for more meaningful competition when it dawns on those coming back that the shirt is not exclusively theirs any more.