And that's what makes these back-to-backs so fascinating. They cannot decide the pools but they can for sure go a long way to determining the outcome.
If Munster win today, it guarantees them nowt, but their destiny remains firmly in their own hands. If they lose, they're still in contention.
But if Scarlets lose, they're a busted flush, but only in Heineken Cup terms.
So much at stake today for sides who are mirror images in so so many ways that for true rugby fans need no elaboration.
Munster will know they came away from Parc Y Scarlets with a four pointer that could so easily have been one. And it has to be hoped that that awareness will make them ever so careful going into today's game.
Because they'll need to be.
Because Scarlets will believe that if they tighten up a little in defence, cut out wayward kicking, sharpen up their cutting edge, then with the Maestro at 10, they can put themselves right back in the mix to reclaim those three points they think they gifted Munster last weekend.
Whether or not they can will be determined, like it or not not, by whatever latitude Ronan O'Gara, Paul O'Connell, Donncha O'Callaghan et all allow them.
Munster: D Hurley; J Murphy, K Earls, L Mafi, S Zebo; R O'Gara, C Murray; W du Preez, D Varley, BJ Botha; D O'Callaghan, P O'Connell capt; D Leamy, N Ronan, J Coughlan; Replacements: D Fogarty, M Horan, S Archer, D Ryan, T O'Donnell, T O'Leary, I Keatley, D Barnes.