Only once before have the Lions won a series in New Zealand and having come here with three days preparation, a suicidal schedule and being all but written off after two games, a test series triumph would be an incredible achievement.
No one gave them a chance so if they pull it off, it is easy to imagine the legend of 2017 growing to ludicrous proportions. Their squad will return home heroes, the coaching staff anointed as the smartest there has ever been and new claims made about the power base of world rugby having shifted North of the Equator.
It will be an incredible achievement all right if the Lions win. Buying into the rest of it would be a stretch, however.
But there is, perhaps inevitably in this age of event magnification, a seemingly insatiable appetite to believe the third test between the All Blacks and British Irish Lions is a career-defining moment for one and all.
It's really not. Some careers will be advanced by victory but not defined. Lions coach Warren Gatland will boost his standing immeasurably, but what if he returns to Wales and sees them tumble down the rankings and bomb at the next World Cup? How then will a series victory define his career?
And some careers will be dented by defeat, but not defined. The All Blacks legacy will have a chip taken out of it, but won't be broken by losing.
Hansen has been involved in two successful World Cup campaigns and has guided the All Blacks to a 90 per cent success rate.
Everyone reckoned he had built the most dominant team in history between 2012 and 2015 and then took them to another level last year.
A series defeat to the Lions would be disappointing. It would be a pea under the mattress of the princess but it would be without any rationale or foundation to start suggesting a series defeat is reason to recast Hansen as a coach who couldn't win anything or failed at the biggest hurdle.
Likewise, should the All Blacks win, it won't change the fact they are a young, inexperienced side who may have more than a few challenging moments to face in 2017.
The pressure won't lift for the All Blacks if they win any more than it will increase should they lose.
A Lions series victory will be something to cherish, but it won't be a reason to start believing they have reached some kind of apex and have nothing left to prove.
In a few weeks they will be off to Sydney to face a Wallabies side that for all their troubles, will be an enormous handful. After that comes a much improved South Africa and basking if the All Blacks go into those game either basking in the glory of a Lions victory or sulking about a defeat, they really will be inviting suggestions they are on a downward spiral.
It's an inconvenient truth for a world increasingly used to instant gratification, but legacies don't rise and fall overnight.
That sun will come up either way on Sunday but from a New Zealand perspective, it will appear that little bit brighter and warmer if the All Blacks have won.
