In the past they have lost games they should have won. This season however, they have won games thay had no right to win, except for the fact that they now have, committment, team spirit, self belief and a edge to their play that, added to a high skill level, leaves them up there right now with the best of northern hemisphere rugby.
They really came of age in the final against Munster.
A missed penalty in the opening minute, seven points down after six, a player down after twenty and 12-6 down at the break. They went 15-6 behind and then delivered a Munster-type performance to come back and rightly claim the spoils.
" In the past people questioned their courage", said a charged-up Matt Williams afterwards, " I never did. And today they've answered those people in the best possible way. They were asked to dig deep and they did. I hope now they get the credit they deserve".
The Australian has to accept praise for his part in their success. The players were there for a while but Williams introduced three vital components, Spooner, Gleeson and Confidence.
It's just two seasons ago that Leinster led Llanelli 21-0 at half time in a vital European Cup game only to end up losing 34-27 and up to yesterday the memory of Reivers in Donnybrook still haunted. But now Williams has cobbled together a side that can compete at any level.
Victory in the Celtic League final sends out a clear message. It's the first trophy Leinster have won in the professional era. It won't be the last. And there is a bigger prize on offer. One that Leinster supporters can realistically dream of seeing being paraded in Donnybrook later this season.