There are certain positions in rugby where size matters. It really does and nowhere more so than lock. There are big men and really big men.
In fact these days are there huge men who can play there, men such as Ireland's Devin Toner who is 2.10m and 125kg.
That size mattered at Soldier Field. Ireland had it, the All Blacks didn't and it told. The story of the game can't be simply that Ireland had more height and weight in their second row, but it was a significant contributing factor.
There's no point looking back and wondering what might have been. There is, however, legitimate grounds to project forward and hypothesise that with - as is likely - both Brodie Retallick and Sam Whitelock available to play in Dublin, the All Blacks will be a different team.
Different in many ways, not the least of which is that these two are in the really big men category. Whitelock came into test football as a 2.02m beanpole. He was 108kg. Now he's 122kg and every bit the same natural athlete.
He leaps as high as ever did, can generate the same head of steam when he gets going it's just now, when he collides with things, he almost always comes out better off.
Whitelock has a presence. No one can miss him. Equally hard to miss is Brodie Retallick who is often described as raw-boned and yet there is 121kg of him and he stands a centimetre higher than his locking chum.
As a combination, these two have become the best in the world. Maybe they have been for more than a year and without their size and considerable range of skills, the All Blacks weren't the same team.
No one clatters up the middle of the field with more impact than Retallick and Jerome Kaino, try as he did, couldn't convert to that role in Chicago.
With Retallick back the effect will be two-fold for the All Blacks: they will have the best middle of the park ball carrier and one of the best, if not the best, wider destructive force with Kaino resuming his natural role at blindside.
No one attacks the opposition lineout quite as well as Whitelock. When he and Retallick return, the All Blacks lineout will have potential to be a weapon rather than the near liability it occasionally was.
But what Whitelock and Retallick also bring is an intangible sense of the All Blacks being intimidating. Size does that - gives the pack ballast and genuine power in the engine.
Of all the negatives to come out of the first Ireland encounter, the one that would have produced the greatest sinking feeling for the coaching staff was that the All Blacks were being bullied.
Physically and mentally it felt like for long periods of the game Ireland were confident they were tougher, more forceful and entitled to play in front of the gainline.
Each lineout blunder intensified that feeling. Each turnover forced when ball carriers couldn't get to ground, intensified that feeling.
It all comes back to size. It all comes back to the undeniable truth that Retallick and Whitelock are, literally, a massive part of this All Blacks side.
When they return together they won't be a panacea as such, but they should go a long way to fixing many of the real and perceived areas of weaknesses the All Blacks had in Chicago.