Call it the umbilical link between fans and players alike, forged as it is on the richest of rugby traditions. Call it the X-factor.
Perhaps it is partly indicative of second or third city syndrome, and happens the world over when they take to the capital for an expression of their identity. Add in Munster's six-year odyssey, culminating in a fifth semi-final and now a third final, and it really is quite a potent mix.
Anyone who was lucky enough to be at Lansdowne Road on Sunday can testify that the sheer sense of occasion was everything one could have expected. The atmosphere, the scale of the colour, the deafening, tumultuous roar that greeted both teams and which sent a shiver up your spine, the heady excitement of those opening 30 or minutes when Leinster were trying everything in their power to strike from distance while repelling the remorseless red wave.
As ever, Paul O'Connell and Ronan O'Gara were barometers of Munster's wellbeing. It is said that Superman wears Paul O'Connell pyjamas at night-time, but O'Gara candidly spoke afterwards of a sleepless night before the game and feeling sick all morning such was the onerous responsibility on him and his team-mates.
O'Gara is a bright, thoughtful lad, but the constant eulogising of his Puma rival at Leinster, especially when their performances were sometimes compared in terms of extracting the best out of pretty much the same backline outside them, would have hurt. As with O'Connell, O'Gara likes to be the best, wants to be the best.
Sunday was his and Munster's day. In years to come, it will be reflected upon as something of a benchmark in Irish rugby history. The day Munster went to Dublin in tribal force and their pack, especially, left a marker.
Far from fazed, they absorbed everything the day meant, fed off it and produced a performance that was in its way well-nigh flawless. It helped that they kept their game relatively simple, as is their wont. It brought to mind Nathan Hines' almost dazed yet admiring post-match mantra about Munster's "pressure game". It is tailor-made for pressurised, cup ties like Sunday's, without recourse to chasing for bonus points or anything like that, and as Matt Williams outlined in these pages yesterday, it is applied in three ways, through possession, position and points.
The quality of their primary possession was exemplary, they retained it through the phases even when going wide, and O'Gara kicked expertly for territory when they felt the need arise. On the few occasions they turned down potential three-pointers, they did so with a clear purpose in mind by kicking to the corner and setting in motion their famed lineout maul.
It enabled them to strike the game's first telling blow, even if not the knock-out punch, when Leinster, on the ropes, bravely hung on around the hour mark.
Leinster were largely left to live off scraps, but they actually had a degree of possession. However, it wasn't nearly as clearcut how exactly they intended constructing a performance and with that, a victory. Not helped by having to calm Felipe Contepomi down, they looked more muddled.
The restarts, literally from the game's first kick-off, are understandably held as an example of how the tone was set. But as telling as any was the one Jamie Heaslip gathered and took back into contact. Contepomi had just opened their account to make it 10-3 after briefly getting their lineout going and generating some momentum and patterns.
Contepomi opted for a wide, all-or-nothing pass to Gordon D'Arcy on the right wing, but he was patrolled into touch by a well-populated blindside defence. Possession and position had been conceded, and when Cameron Jowitt tugged at Paul O'Connell from the ensuing Jerry Flannery throw, O'Gara tagged on the points. Leinster's hard-won opening score had been chucked away. The pressure was back on.
When Munster received Contepomi's second-half kick-off, O'Gara returned it to inside halfway, Brian Blaney's ensuing throw was crooked, and Leinster spent the next four minutes tackling in their own half.
Of course, Leinster's approach this season has been thrilling; their performance in Toulouse arguably the high point of the tournament for sheer verve and skills conducted at pace. At the heart of this rejuvenatory season has been Contepomi, and it would far too fickle to just dismiss all of that in the light of one defeat, albeit one that will hurt players and supporters alike for many a day. Munster had to start somewhere too, and one hopes Leinster's new-found legion of supporters stick with them.
Sunday's semi-final exposed this comparatively callow Leinster team to the rarified atmosphere of an intensity akin to a Test match, far removed from NPC or Super 14 rugby. They have signed Trevor Hogan and Stephen Keogh, although tellingly, one was on Munster's bench and the other didn't even make that. The same, admittedly, would probably be true of others in Sunday's starting pack. They still look like they need another warrior/leader or two up front.
But with games like Sunday's come experience, as Munster will testify. And O'Gara sounded a cautionary note when stating that Munster cannot afford to look upon last Sunday as a final, or a peak, while scaling those heights will be more difficult a second time.
Forget too, the purists' dismissive verdict on Biarritz's semi-final win over Bath, or indeed Sale before that. They look to be playing within constraints of their own making, but no less than Munster against Perpignan, Biarritz did what they had to do to win a cup match, especially after torrential rain.
Nor do Munster have a monopoly on magnificent obsessions. Biarritz, after successive semi-final defeats and three manifestations of Basque pride in full houses in San Sebastien, have theirs too. They also have power aplenty up front, more than Leinster have. It will be a brutal, bruising affair. It will be a cup final.