All Blacks captain Kieran Read. Photo / Photosport
Contrasts create friction. Ireland's positive recent record against the All Blacks creates the obvious point of friction but boil that down further and it exists more so within their playing styles.
There are no more two contrasting teams remaining at this World Cup, no more contrasting quarterfinal. Even South Africa,with the likes of Cheslin Kolbe, are more adventurous, more enterprising, than Ireland.
The contrast that separates Ireland and the All Blacks comes from a guiding philosophy to be prescriptive or reactive, to stick stringently to patterns or to embed structures but ultimately play what you see and embrace freedom of expression.
By nature, New Zealand rugby players want to use the ball. In many respects the challenge is to temper those instincts somewhat, to get players thinking more laterally for the team, to pick their moments, rather than simply having a crack at all times from anywhere on the field.
Damian McKenzie and Jordie Barrett are classic cases of this evolution.
New Zealanders grow up throwing the ball in the backyard, emulating idols' signature traits.
More often than not those involve a step, offload, some freakish play. They almost always involve attack.
Ireland can't be blamed for sticking to their strengths. These carried them to the top of the world last year. But after starting three games in Japan neither of their preferred wingers, Jacob Stockdale and Keith Earls, have scored a try.
Jordan Larmour is one of the most skillful attacking talents in the northern hemisphere game. Despite a brilliant display against Samoa in Ireland's last match, he could well be replaced at fullback by the safe option in veteran Rob Kearney.
Joe Schmidt's game is based almost exclusively around set piece dominance, ball retention, Conor Murray's box kick when Ireland are under pressure or tire of setting rucks, and Andy Farrell's defensive blueprint.
They will attempt to frustrate the All Blacks by starving them of ball. This approach is predicated on the premise that the All Blacks are lethal from turnovers and on the counter. Control the ball and limit mistakes, and Ireland hope to limit the All Blacks ability to strike.
When they get it right, Ireland are very good at this formula. It's not pretty but it's effective.
Mistake-free rugby translates to no risk rugby. Minimal offloads, few passes, limited width, and always, always sticking to the pattern. It's prescriptive. Ingrained, even.
This is where the great intrigue arises. The All Blacks differ so drastically from Ireland because they will continue to play their natural game as if they were kids in the backyard.
They, too, have structures, pod formations and pet plays for certain parts of the field. But they are always encouraged, even in a knockout situation such as this where the stakes are so high, to break from those confines and have a crack.
Unlike Ireland, the All Blacks have much more flexibility to play off the cuff. Ultimately this makes them that much more difficult to plan for.
Traditionally the switch from the pool stages to the knockout arena brings a more conservative brand of rugby.
But for the All Blacks, this week the message remains the same. Don't tighten up now. Back yourself on the grand stage. To do otherwise would be to waste the inherent brilliance of Beauden Barrett, Richie Mo'unga, Anton Lienert-Brown, Dane Coles, Ardie Savea and Sevu Reece.
Where Ireland are prescriptive, the All Blacks want to be reactive. This approach, this contrast, brings far greater risks but, potentially, far greater rewards too.
"It's where you go when you're under pressure," All Blacks assistant coach Ian Foster said. "That's the exciting part about this stage of the tournament. We still want to be confident enough to play the pictures that we see and trust the guys to execute and make decisions but sometimes pressure can do funny things to people and you can eliminate all the risk out of your game.
"That's the balance, that's the exciting part about knockouts. It's about getting your players really excited about if they see pictures, are they allowed to execute? Yes they are. It's certainly something we want to continue doing on our behalf."
There's no right or wrong approach but after 80 minutes in Tokyo this weekend, one clear style will prevail.