LEINSTER captain Leo Cullen is a careful man, careful not to antagonise the Cardiff Blues, careful not to give a vibe of over-confidence which would be immediately interpreted as arrogance on the other side of the Irish Sea.
Thirty-four-year-old Cullen has been too long in the game and has seen too much to take anything for granted despite evidence to the contrary.
The Cardiff Blues don't have a history of success in Europe or their two most dominant players in Wales captain Sam Warburton and centre Jamie Roberts.
Gavin Henson, that 'enfant terrible', has been sacked in the build-up as The Blues come into this one after a 31-3 hiding from Glasgow Warriors in the PRO12 League. They are in the precarious position of looking for form.
"We know their players and we know the damage they have done to Irish teams at different stages over the last number of years," issued Cullen.
"We've gone into games ... I remember Perpignan in 2003. No one gave them much of a chance. We had beaten Biarritz in the quarters -- they were the so-called big team at the time.
"Not many people knew much about Perpignan. We all know the result, what happened that day. You've always got to be on your guard."
Coach Joe Schmidt's policy of rotation has generated a looking-over-your-shoulder motivation for the players. No one is completely safe.
"There is a good competitive edge in the squad and, obviously, everyone wants to be playing. Places are hard to come by in the starting team," added Cullen.
"We have a certain eye on what the opposition is doing. It is not the be-all and end-all. As well, you have to have a lot of focus on what you're doing yourselves.
"It is important that we get our own basics right in the game and that mentally we are in the right place when we go to play.
"Sometimes, it is a lot of fuzz about what the opposition are gonna' have.
"It is important we spend the majority of time focusing on what we're going to do."
There were just 500 tickets left for sale yesterday, all returned by Cardiff. It is a safe bet that they will be gobbled up before the start of play tomorrow at The Aviva Stadium.
Leinster have not lost at the national stadium. Munster, Clermont-Auvergne, Toulouse and Leicester Tigers have all been beaten there.
"The way the fans have bought into it has been phenomenal. As a place to play, it is great. The colour, the flags and the noise -- it is a really special atmosphere.
"Reputations don't really count for much.
"If we're not quite on our game, Cardiff have experienced, big-game players.
"They are not going to care about reputation."