As a New Zealander, Lions coach Warren Gatland knows that a tour down this way comes with unique physical demands that can't be met by those players who don't have the mental resilience to persevere through anything and everything.
His conviction that he needs genuine warriors who have either previously held up in New Zealand or at least experienced and thrived in some kind of pressure-filled rugby environment, will be seen later tomorrow night when he names his 37-man tour party for the Lions' 10-game tour of New Zealand.
The squad should tell a story of what Gatland thinks the tour will be all about: it should illustrate that on all the toughest calls, he has deferred to those men whom he feels carry the hardest edge. He'll be picking players whom he believes will see the challenge of playing the Blues, Crusaders and Highlanders within 10 days of each other as inspiring rather than madness.
He is spoilt for choice at hooker, lock and loose forward and the men who actually make it out here will most likely be those who Gatland feels will pick themselves off the turf after they have been cut in half by Jerome Kaino and carry the ball even harder the next time they have it. It will be a tour for hard heads, tough nuts and unbreakable types who will relish the combat, the mental seige that comes with playing in this part of the world and finish each game hungry for more.
The Lions know that in Brodie Retallick and Sam Whitelock, the All Blacks have the best second row pairing in the world game - a combination that comes with natural skills and a nasty side. Those two epitomise the All Blacks - they are relentlessly tough, athletic, skilled and disciplined: capable of playing well within the laws while emanating a vibe that says they would be willing to go outside them if needs be.
Players who have been here and faced that ferocity in New Zealand's back yard, have a distinct advantage and that's why the number of Scots in the party most likely won't reflect their resurgence. None have ever played in New Zealand so the likes of Richie and Johnny Gray may miss out to Ireland's Ian Henderson, England's Courtney Lawes and Maro Itoje and Alun Wyn-Jones of Wales. The Welsh fetching duo of Sam Warburton and Justin Tipuric competed strongly in New Zealand last June, while the two Irish loosies, CJ Stander and Sean O'Brien have battled gainfully against the All Blacks in the past.
Mental toughness is applicable not just to the forwards. The backs will need it to and that might be why reports out of the UK suggest England's Jonathan Joseph and George Ford aren't going to be included. They are both supremely talented but they blew hot and cold in the Six Nations, hinting at some kind of fragility somewhere in their make-up.
Where, perhaps, most will be gleaned, is in Gatland's thinking with England captain Dylan Hartley. The New Zealand-born Hartley is as tough as they come, fits the bill of being willing to go to battle. But he's prone to overdoing it - he's been ill-disciplined and wild on too many occasions and if he's included it will signal just how much fire Gatland wants his team to be breathing.
Hartley will confront, he will niggle and he will, to some extent inspire those around him with his aggressive mind-set that shows no fear. But there is a fine line between showing mental resilience and being shown a red card.