It's by seeing McCaw give so much that they are forced to ask whether they are willing to do the same. They can't kid themselves any more: once they see that they are not on the same level they have to decide if it's within them to even try to give that much.
It's apparent that most of this All Black side have taken on the challenge of digging that bit deeper. They can't match McCaw, but they can at least try and it's that little appreciated fact that has been such a big part in the All Blacks' phenomenal record since they won the World Cup.
The ice-cool temperament of McCaw and the other leaders has been important. The ability to stay calm, trust the gameplan and make good decisions has been another factor. And it goes without saying that the talent of the players combined with the tactical vision of the coaching team has been critical.
But 23 players all willing to go to the edge of their psychological and physical capabilities: all 23 of them ready to go that bit further than the opposition ... that matters.
That makes the difference between a good team and a great team: that is primarily why the All Blacks have not, since the World Cup, lost to teams they should have beaten.
England earned their victory in 2012 - played the All Blacks off the park. South Africa scored some sensational tries at Ellis Park and took the game by playing better rugby this year.
And that's what McCaw's captaincy has done - coated every possible soft spot in heavy duty armour. He's made the All Blacks almost unbeatable even on the days when they are playing badly.
When players are willing to cover that bit more; to get on their feet that bit quicker and empty the tank just one fraction deeper all because they are trying to be sure they can look the skipper in the eye, it makes the All Blacks an incredibly tough side to beat.
If there has been a theme in 2014, it has been the art of winning ugly and there is no greater testimony to his value as a leader than the All Blacks' quite uncanny ability to battle fired up opposition, their own shortcomings and, far too often this season, fairly awful officiating.
The clock doesn't have to be wound back very far to find a time when the All Blacks knew only how to win when it all went right for them.
Not now. McCaw doesn't let the potentially loseable become the actual loseable.
His achievement of 100 tests as captain may never be surpassed. It's just too hard to even begin to know how to explain how he has managed that and what it has taken for him to survive 10 years in the job.
While his career inevitably has a few more twists and turns left, it would be silly to not state categorically that he is the best captain the All Blacks have ever had. He is the best captain the world game has ever known.
Captaincy milestones
1st test
26-25 Wales, Cardiff Nov 20, 2004
23rd
18-20 France, Cardiff, Oct 6, 2007
25th
37-20 England, Eden Park, Jun 14, 2008
50th
20-10 Australia, Christchurch, Aug 7, 2010
66th
8-7 France, Eden Park, Oct 23, 2011
75th
32-16 South Africa, Johannesburg, Oct 6, 2012
