He must have meant their confidence in being able to deal with and dominate the European champions. This is a factor that Leinster can exploit.
"We really rattled them only to come up short at the end," said Leinster skills and kicking coach Richie Murphy.
"The lads really, really put everything they had into it out there on the pitch. It was fantastic to see them apply themselves to the game-plan."
It was also apparent that Leinster's ploy to hold onto the ball and drain the optimism out of the Stade Marcel Michelin crowd was the right one when it would certainly have been easier to play for territory.
The best news for Leinster is that their scrum went into overdrive to splinter Clermont as the game wore on, with Springbok Heinke van der Merwe a possible addition to the squad this week.
The bad news for the French is that Thomas Domingo will not be back for the return leg. Vincent Debaty has never been a reliable scrummager. He was ruthlessly exposed by Mike Ross.
"Our guys work really hard on that area. They put a lot of pressure on the Clermont front row. I don't think we got everything we deserved from it either," said Murphy.
"It was a fairly even contest in the first half. But we turned it around in the second, going on to dominate them. We just didn't get the penalties we wanted out of that."
There is great room for improvement at the lineout where replacement hooker Richardt Strauss was wayward in his throwing, twice flighting the ball over the top in attacking positions.
The positive there is that Strauss is a very accurate thrower and it will not take too much to put that right next Saturday.
Flanker Kevin McLaughlin suffered a bang to the head, received treatment and managed to walk off under his own steam. He will be monitored this week.
The form of full-back Ian Madigan and centre Andrew Goodman were other positives. They were not the weak links forecasted before the tussle, Madigan for playing out of position and Goodman for being new to the Leinster way.
"Both of them did very well," added Murphy. "In fairness to them, they prepared well in the lead in to the match and slotted into the backline very comfortably.
"Mads has been very good in all the matches he has played at full-back for us. But this was a big step forward for him because he did all that was asked of him to be very impressive.
"Andrew applied himself physically. He carried the ball well against what is a top class international centre pairing in (Wesley) Fofana and (Aurélien) Rougerie."
While Clermont took the battle, they have not convinced they have the tools to win the war. Leinster have a psychological edge. Cotter knows it. Joe Schmidt knows it.
Now, Leinster just have to do it all over again. This time they must emerge as winners or face up to the heartache of losing their crown.