The theory that every team has a weakness will get its sternest test, from an Irish point of view, tomorrow, when former Shamrock Rovers player and manager Liam Buckley has to try and find a way to do what no one else in the country has done for 14 months: outwit his former club.
Since September of last year, the Hoops have played 26 games of domestic football without defeat. The only side to overcome them in that time are AC Milan, 2-0 winners at Tallaght Stadium in the Europa League in September, their status underlined by the fact that the Italians' best player that day, the sublime Turkish playmaker Hakan Calhanoglu, has been earmarked as one of the January signings for Manchester United deemed capable of turning their season around, albeit with a €40m price tag attached.
Sligo were beaten 4-0 on their last visit to Tallaght Stadium, and the task for Buckley, not long after their midweek cup quarter-final win over Derry City, is to counter that, the Rovers boss admitting that cutting out their own mistakes is a start, but not enough.
"They're not unbeatable - that said, they are the best team in the league and we have our work cut out to get a result," said Buckley.
"If we play them X amount of times, we win a smaller percentage than they would. It's going to be tough, but we will have some sort of plan to give us a chance of getting something out of the game. Otherwise there is no point in going up.
"They have a style of play that they have stuck with, week-in, week-out. They play out from the back and have a passing style. We have got to ensure that we don't throw up as many silly chances as we did the last day, from a defensive point of view.
"We've looked back at the videos and we were just poorly positioned. That said, I have no doubts that they will cause us problems. We have got to curtail them," added the Sligo boss, who shows his allegiance to his current employers by only referring to tomorrow's opposition as 'Shamrock Rovers' and not 'Rovers', because to Sligo folk there is only one real 'Rovers', the other side are, naturally, the 'Shams'.
But if the Bit O'Red are to get through they'll need a bit of steel.
For captain Garry Buckley, who has happy cup memories of his own from his Cork City days, it's about restricting the holders and league champions.
"If they score early, or score first, that's when their tails are up and they're playing their best football, their best players come out. If you keep it tight, compact, frustrate them, their game starts to diminish a bit, the heads go down," said Buckley, successfully converted from midfield to central defence since his move to Sligo.
"That's the game we need to look at. Frustrate them, stay in the game for as long as possible. Once you're doing that, you're giving yourselves a chance," added the Sligo defender.
While the Connacht club travel east to try and create the upset needed to earn them a cup-final date a week tomorrow, Dundalk will be aiming to shrug off their European woes and focus on making it to the decider for the sixth season in a row, Athlone Town standing in their way.
Dundalk coach Shane Keegan admitted after their 3-1 loss to Rapid Vienna on Thursday that the Athlone camp would be "licking their lips" at the prospect of playing the Co Louth side so soon after a bruising game, a match which had off-field consequences, too, as Dundalk were moved to issue a statement last night, hitting out at the "vile" racist abuse on social media directed at a member of their squad.
For defender Andy Boyle, tomorrow has added importance given the side's struggles in other competitions.
"The Athlone game is massive, the league season hasn't gone to plan and we haven't put ourselves in the mix to get out of the group stages in the Europa League, so Sunday becomes massive, if we can get ourselves into the cup final," said Boyle.
"It won't be the same this season with no fans there, as it's always such a huge occasion, one of the dates you look out for at the start of the season. When the FAI Cup final comes around you want to be in it, and we have a good opportunity to get into it."