Those who attempt to climb Mt Everest talk of the dead zone. It's the point where oxygen becomes insufficient to sustain human life.
Some climbers thrive in this zone. Others feel the life draining out of them and they don't make it back home. They succumb to it.
The Crusaders are champions because they thrive in rugby's dead zone. They know how to win big games: how to squeeze a little bit more out of themselves when the last thing they felt like doing is digging deeper and scrapping harder.
They are fighters. They are believers. They are champions. In what has been one of the great three months of rugby in any age, they have delivered one of the great campaigns.
Super Rugby Aotearoa was short by comparison with all its predecessors. But give the Crusaders players a few weeks to think about it and they will agree that of all the various iterations in which the tournament has existed, the 2020 version was the toughest of them all.
The rugby was endlessly tough. It was brutal. It was beautiful and it was phenomenally competitive. This was eight test-match intensity games on the hoof.
The emotion was always high. The pressure constant and the sense of the world watching never went away. This was a tournament that put New Zealand's rugby in sitting rooms around the world – a daunting place to be for that length of time.
There were no Rebels or Sunwolves to break things up. No shadows in which anyone could hide and nothing came easy as almost every game was still in the balance deep into the death zone.
Those last 20 minutes are rugby's dead zone. That's the time when the oxygen is running short. When the body is starting to shut down – feeling the impact of all the collisions, all the metres covered.
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That's the time when the best teams find a way to keep going and that was the key to the Crusaders' success in Super Rugby Aotearoa – a near faultless ability to lift their intensity in the final quarter of every game they played.
They were barely hanging on against the Highlanders as the game reached the last 20 minutes. They were staring at the thing they didn't want to be staring at – a winner-takes-all showdown with the Blues at Eden Park in the final game of the competition.
But it looked like that would be their destiny. The Highlanders were refusing to buckle. They had a nine-point lead and their confidence was growing.
The home side, on the other hand, looked like the nervousness which had been apparent in the first 20 minutes had taken root again.
The pressure was bearing down on them. The clock was getting away from them and the Highlanders were on top of them.
The game was slipping away and then in a three-minute blast, the Crusaders were suddenly leading.
They had found a new level at a time in the game when teams so rarely find a new level. Two tries came to George Bridge because they had the ability to break a Highlanders defence that had brilliantly manned the sea wall but couldn't hold on when the pace surged.
It was a killer blow. The game in the Highlanders pocket and then two lightning strikes and it was over.
This is what separates the Crusaders from other teams – a quite remarkable ability to lift the speed, intensity and accuracy in the last quarter.
No one else knows how to soak up pressure like they do and find a way to make themselves stronger.
They refused to stop believing against the Highlanders. They never lost their composure or certainty that the game would swing their way.
Other teams would have imploded. They would have let their doubts engulf them and fatigue wash over them.
Not the Crusaders though. They brought Sione Havili off the bench and he thundered into contact hard enough to convince others to follow him.
Richie Mo'unga kept making the right passes, pulling the right strings and space was opening up. The half chances they couldn't take before, they were finishing in the last quarter and adding to remarkable statistic that their most profitable points quarter all season has been the fourth.
They have come alive in those final 20 minutes all year. Memorably against the Blues a few weeks ago when Mo'unga sparked a revival by reclaiming his own kick-off.
And then again against the Highlanders to claim their fourth successive title and one that they will relish more than the others because this one tested more than they have previously been tested.
This one was won exclusively from the dead zone.