And the figure four also looms large for Stade Francais Paris - in their case hoping it is fourth time lucky in their bid for a European title - following their last four 25-22 triumph at French rivals Perpignan.
Sergio Parisse and his team-mates suffered heartbreak in the 2011 tournament final in Cardiff when Harlequins edged them out 19-18 and the pain is still there.
"We were a bit unlucky in the final against Harlequins a few years ago and that defeat is still in our minds," said Parisse. "We have worked hard to reach another final."
That single point reverse followed the agony of two Heineken Cup final defeats, 34-30 to Leicester Tigers in 2001 and 18-12 after extra time to Toulouse in 2005.
It all adds up to their three near misses being by just 11 points overall - an average of less than four points per final.
And here comes another four - Leinster and Stade Francais Paris have already met that many times in Heineken Cup contests with the French club ahead 3-1 from their Pool clashes in the 1998/99 and 1999/2000 campaigns.