Leinster have more than enough recent Champions Cup heartache to deal with but the memory banks store plenty of older pain in that department as well.
Back when Toulon were in their heyday, there's a particular wince-inducing passage of play that sticks in the craw.
Leinster took the then back-to-back champions into extra-time in the 2015 semi-final in Marseille and were trailing by three points when they won a turnover in midfield just before the end of the first added period.
Toulon were operating with 14 players at that point with Ali Williams in the bin.
Ian Madigan, who kicked 15 points that day, fired a loopy pass out wide for Ben Te'o but, as if he needed it, the trajectory gave Bryan Habana a split second to spot the chance and the South African intercepted and raced home.
Sean O'Brien managed a late try but the Springbok had already landed the killer blow in a 25-20 win.
It took Leinster another three seasons to scale the European summit again. It felt like one that got away.
Toulon were a star-studded outfit at the time, boasting Frederic Michalak, Mathieu Bastareaud, Matt Giteau and Leigh Halfpenny among the backs, the forward pack contained Guilhem Guirado, Carl Hayman and Bakkies Botha.
The Galacticos would go on to beat Clermont in the final in Twickenham.
"I remember the intercept unfortunately," Leinster wing Tommy O'Brien, who was 16-year-old student in Blackrock at the time, said when asked for his memories of the rivalry.
"Ian Madigan probably won't be loving the whole build-up this week, I'm sure that'll come up a couple of times.
"But yeah, I remember watching any of those games, they were an unbelievable Toulon side.
"I remember Leinster kind of always put it up to them and maybe fell short a couple of times.
"But we know the challenge it's going to be, it's going to be pretty similar this week."
That was the third meeting of the teams and Leinster have never beaten Saturday's opponents.
Toulon, then under Bernard Laporte, won a quarter-final 29-14 the year previous and beat Leinster 24-9 and 20-16 in pool-stage encounters in December 2015.
"We know Toulon have a lot of history in the competition as well and they love the competition," added the 27-year-old Ireland winger.
"Some French sides maybe might prioritise the Top 14, but we know that their history, they've had a lot of success in this competition.
"We know how much it means to them, how much it means to their fans. So I think hopefully it should lead to an unbelievable game and an unbelievable atmosphere on Saturday."
Pierre Mignoni's men sit eighth in the Top 14 after last weekend's 52-26 win over Bayonne, their 11th win from 22 games in a mixed domestic season.
On the European front, they finished second in Pool 2 behind Bath, who face champions Bordeaux-Begles in the other semi-final (Sunday 3pm Irish time).
They started their campaign with an away defeat to Edinburgh before beating Bath, Munster and Gloucester to reach the knock-outs.
Victories at home to Stormers (28-27) and away to URC leaders Glasgow (22-19) set up Saturday's first Champions Cup semi-final in 11 years.
"We know the history," Toulon winger Gael Drean, who is the competition's joint top try-scorer with seven, said of the club's pedigree which also includes the 2023 Challenge Cup title.
"When you sign here, you know what's come before you.
"It's something that will forever be etched in the club's folklore.
"For the fans and everyone who follows the club, it's great."
"A club like RC Toulon is known internationally for everything they've achieved, so it's great to be back at this level.
"We'll see how important the Champions Cup becomes to us come the end of the season, but it has certainly afforded us more wiggle room in the league — long may it continue."
There's a real international feel once again to the French outfit with players from England, Italy, Georgia, Scotland, Argentina, New Zealand and even an Irish-born famous son among their number.
Prop Dan Brennan (below), son of former Leinster, Toulouse and Ireland forward Trevor, may feature for the French side in Dany Priso's absence.
There are concerns about the fitness of forwards Charles Ollivon, David Ribbans, Lewis Ludlam, Swan Rebbadj and Brian Alainu'uese, who missed the Top 14 win at the weekend but the team did include Les Bleus stars Jean-Baptiste Gros, Baptiste Serin, Melvyn Jaminet and Grean.
Italy out-half Paolo Garbisi and centre Nacho Brex also started, while former Munster midfielder Antoine Frisch was on the bench.
France internationals Priso and Gabin Villiere, and Marius Domon are unavailable through injury.
"They've got a very strong setpiece," said Leinster scrum coach Robin McBryde.
"They've got Kyle Sinckler, Dave Ribbans and Ollivon as well. They all play a roll to create that style of pace they've got.
"[Esteban Abadie, below], has got the most lineout steals in the Top 14, Ollivon is a menace in the air as well."
In the backline, Brex has impressed Leinster and Ireland centre Garry Ringrose and the pair may face off directly at Aviva Stadium.
The Italian scored an incredible solo match-winning try against the Warriors.
"He's an exceptional player," said Ringrose. "As a 13 there are little intricacies to his game that I really admire and appreciate. It's no surprise he's going as well as he is, consistently for Italy and for Toulon.
"His defensive reading of the game is exceptional. You see him on attack and he's taken it to a new level - his try he scored against Glasgow in the quarter-final is a case in point really."
With last year's reverse to Northampton a notable exception, these home semi-finals are games that Leinster usually win.
However, with six URC defeats already to Leinster's name this season, Toulon, 11-point underdogs, will come with confidence and feel they have a real chance of an upset.
