Alan Quinlan: The rivalry between Leinster and Scarlets has been simmering nicely but could reach boiling point today
Familiarity breeds contempt and it doesn't take long for frequent showdowns on the rugby pitch to develop into fully-fledged rivalries.
Today, Leinster take on Scarlets for a 32nd time, although the prize on offer at the Aviva makes this contest comfortably the most important in their feud to date.
When Ireland got the better of Wales two months ago en route to their Grand Slam success, half of the 46 players involved across the two match-day squads plied their trade with Leinster or Scarlets.
If you add the pain that the Welsh side inflicted on Leinster with their shock 27-15 Guinness PRO12 semi-final win in Dublin 11 months ago, it's easy to understand why a testy rivalry is developing between these two outfits.
These PRO14 heavyweights went toe-to-toe twice in the space of three weeks earlier this spring without their vast international contingents but the rivalry wasn't diluted at all in two closely-fought encounters - a 20-13 home win for Leinster and a 10-10 draw in Llanelli.
The animosity between these two has become deep-rooted, and considering their respective domestic strength, this rivalry looks like it's only really beginning.
It was interesting to note last week that the free-talking Kiwi winger James Lowe - man of the match in the aforementioned RDS win in February - has been taken aback by the edge between these two sides.
Lowe, after all, has vast experience of playing in the Mitre 10 Cup with Tasman, a national provincial championship in New Zealand that certainly doesn't lack for parochialism.
"Man, it's exciting - you can definitely tell there's a rivalry between Leinster and Scarlets," Lowe said before his unfortunate omission from the Leinster squad was necessitated by Luke McGrath's failure to overcome an ankle injury.
"I've only been here six months but played them twice and there's definitely a grudge. It'll be good to have both teams with all their internationals actually playing and hitting it out."
Pre-match quotes are generally littered with softening cliches about processes and focus but Leinster v Scarlets has become personal for both sets of players who currently lead the way in Conference B of the PRO14.
Ross Molony admitted as much before hosting the Scarlets in that Round 15 victory two months ago.
"For us, it's about driving that message that this is about us getting revenge, it's about us not allowing a team to come to the RDS and beat us," he said.
It is a measure of the consistency that Scarlets have added to their game, as well some astute recruitment and coaching by Wayne Pivac and Stephen Jones, among others, that they are seen as genuine contenders for Europe's top prize.
Leinster and Munster may have been caught out by their high-octane game in the latter stages of the PRO12 last season but Leo Cullen's side will be prepared for the ambush this time around.
There is always a fear with teams such as Scarlets, who don't have a big budget, even by PRO14 standards, that they could fall away after such a successful season, much like Connacht did after 2016, but they have proven in this campaign, with victories against Toulon and La Rochelle, that they belong at Europe's top table.
Both sets of players will be very familiar with their opposite numbers today and there are a number of contests that will have a major impact on how the game pans out.
The story of Tadhg Beirne has been enthralling thus far and it will be fascinating to see how the Kildare man continues to develop with Munster next season.
But for now, I can't wait to see him go up against James Ryan, another all-action second-row who has followed a much different path to becoming one of the most dominant locks in Europe.
Ryan is more than four years Beirne's junior but has already achieved a Grand Slam in his first eight international caps, while his 26-year-old opponent has only really hit his straps since making the career-defining decision to move across the Irish Sea.
Beirne has been in inspired form for Scarlets this season, evidenced by his nomination for the European Player of the Year gong, and he will be desperate to deliver his best performance of the season against his previous employers this with so many friends and family, and former and future team-mates, sure to be watching with intrigue.
Both of these sides have been lauded for their scintillating ability out wide but the front-row fight will also be telling.
They may be perfect conditions for running rugby, but as Munster and Leinster learned last year, if Scarlets get the edge on you up front you'll be up against it and crucially, it will give their dangerous backline the small window they need to strike.
Scarlets are fielding a Wales front-row in Rob Evans, Ken Owens and Samson Lee, while opposite them is another seasoned unit of internationals with Cian Healy, Sean Cronin and Tadhg Furlong, not to mention Lions loosehead Jack McGrath and the powerhouse that is Andrew Porter in reserve.
There will be a lot of pressure on Jamison Gibson-Park to produce the goods too, not just as he attempts to cover for the supremely talented Luke McGrath, but because in Gareth Davies, he is up against one of the most dangerous scrum-halves in the world.
The breakdown battle also promises to be vital. Generally when we see John Barclay dominate that area of the game - for Scarlets or Scotland - his team prevail.
Dan Leavy will be desperate to disrupt Barclay, Beirne and James Davies in particular, and be a nuisance himself, ably assisted by a talented Leinster forward unit that rarely fails to dominate games.
Very few people seem to be giving Scarlets much hope today but you can be certain there will have been no complacency within the Leinster bubble in the build-up.
Scarlets were behind on many of the key statistics in last year's PRO12 semi-final - such as turnovers, missed tackles, territory and possession - but they made the most of the ball they had and managed to frustrate their hosts at the other end.
Last year's semi-final defeat still stings in Dublin 4 as it further extended their trophy drought, and the Welsh side will have little fear after the European performances they have already produced this season, not to mention the fact that they beat Leo Cullen's men last May playing with 14 men for the majority of the game.
Scarlets are a proud rugby club who are on the rise once again. They still reminisce about their 1972 victory against the All Blacks in west Wales, six years before Munster matched the feat, and this is the club's fourth semi-final on European club rugby's biggest stage. They may have failed to overcome this hurdle on the three previous occasions, the most recent 11 years ago when they fell to the Leicester Tigers, but this group of players have shown they have no fear of the unknown under former police officer Pivac, who appears to be Warren Gatland's successor in waiting.
This should be a cracker, and while I have sided with Leinster to shade proceedings, I expect it to go right to the wire.
And the way both of these teams are developing this looks like being just the latest instalment in a long and storied rivalry.