The strength of a good team is their ability to win a game against the odds. Last weekend's victory would have been mentally and physically tough for many reasons.
Watching the other provinces in their respective games is difficult when your game is sitting last in the pile of the weekend. European Cup weekend will always create dramas and for Leinster, with their first match being a home game, the added pressure to not slip up is very much relevant.
For Matt O'Connor, the victory proved that the result of his consistency in selecting Darragh Fanning and Dominic Ryan over the last two months has been hugely beneficial.
Fanning proved himself at this level with a brace of tries and was unlucky not to make it three while Ryan was constantly destructive and bagged the most important try of the night.
Jimmy Gopperth stood up to the occasion, and the back-line, particularly in the second half, seemed to operate nicely against a Wasps team of pure power and pace.
Leinster are at their best when they disregard the numbers on their back.
If you look from a back-row point of view, there is no difference between a combination of Jamie Heaslip, Rhys Ruddock and Ryan, or Heaslip, Ruddock and Sean O'Brien.
Both back-row combinations would be equally effective and not determined by a number on their back. When you take the Leinster back-line in this scenario, this is when we see glimpses of what Leinster can really do.
Fanning as a winger shows an abundance of enthusiasm to come in off his line and look for ball. This characteristic is infectious throughout a squad and last weekend you had a hungry Gordon D'Arcy, Noel Reid, Zane Kirchner and Ian Madigan.
Not everything went to plan but the hunger for impact was there and, inevitably, when Wasps buckled, Leinster took their opportunities.
Castres are quite the opposite - very dominant in the set-pieces and with a big pack of forwards, they will be keen to slow the game down. From their set-pieces, their South African scrum-half Rory Kockott (now in the French squad) can be outstanding but outside him, they are average and are struggling in the Top 14.
Heaslip proved himself to be the best No 8 in the Northern Hemisphere against Wasps. His leadership over the past seasons has taken a different direction and he has realised that he doesn't necessarily have be all singing and dancing off the pitch. It's on the training field and during games when it matters.
In contact, himself, D'Arcy and Sean Cronin not only break tackles but when they drop themselves into a squat position for the final contact they also pump their legs which gains a minimum five to 10 yards more.
The excitement factor kicks in when you consider the injured players that have to come back - none more than Luke Fitzgerald.
Fitzgerald has an integral part to play in this squad and the sooner he gets game time the better.
With a full complement available to O'Connor, he will be back to making hard decisions in selection, particularly with some of those he has shown faith in.
Travelling away to an already beaten French side is always dangerous, and there were certainly frailties in victory last weekend.
Richie Gray, Castres' second-row and lineout ace, will prove a threat to Leinster in this area.
The defensive pattern Leinster are using in open play is ineffective after four phases - against a team that notices this Leinster will also be exposed.
The victory against Wasps showed that Leinster are not ready to relinquish their grasp on this competition. Home games have to be built on and the team will know that throwing it away next weekend will make it fruitless.
However, the gift of seven days to recover will be vital and selection for next weekend will be the most anticipated to date this season.
Leinster have the ability to beat the French at their own game. If they can do this, we will then see the RDS and the Harlequins Stoop at maximum capacity come December.