Even when he first earned regular selection in 2008, there were doubts. He'd be on one test, off the next. Inconsistency was his curse and it took a "Look, son ..." chat with the All Black selectors at the start of 2010 to begin Kaino's evolution.
They laid it out nice and simple - that they felt he could be something special if he gave himself the chance. That meant looking at his conditioning; looking at his dedication to be the best; it meant giving everything he had and to make the mental commitment to stay behind at training for extras; to tick every box and look the likes of Richie McCaw and Kieran Read in the eye and know he'd worked as hard as them on every aspect of his game.
The evidence of the transition came through in Super Rugby that year. Kaino backed up - big games followed big games and he was relentless. Midway through the season, Blues coach Pat Lam was delighted with the new Kaino.
"He took it really well," Lam said of the little chat earlier in the year. "The one thing you want is honesty and he took it straight down the barrel, if you like, and he's responded.
"In the last couple of years, Jerome has always been in the leadership group as far as off-field stuff goes. I realised this year that for him, it's not a priority, it's about leadership on the field, the strategy side of the game, as a lieutenant to Kevvie [Mealamu]. He's done a lot of work on the game as a whole, rather than just his position. His understanding of that enables him to do his job better and to see the bigger picture."
Such has been Kaino's excellence in the past 18 months that recalling him as a ghost in some tests is not so easy. All that comes to mind now is a rampaging Kaino blitzing half the Canadian pack; Kaino thundering into the Wallabies in the semifinal and then cheerfully patting Australian heads is another memory; so too is the tackle he made on Bradley Davies last November in Cardiff - one where he nearly cut the Welsh lock in two.
Kaino is the omnipresent memory of the 2011 World Cup - not just because he played all but 30 seconds - but because he played so spectacularly well. Maybe he was a little quiet in the final but that could have been due to the enormous defensive shift he put in. It's hard to smash the hard yards with the ball when your side so infrequently has it.
It didn't matter. Kaino was the All Blacks' player of the World Cup even before the final. The players who got close would be Owen Franks, Israel Dagg and Richard Kahui. Franks was a beast - so admirably old school and determined to dent things. Dagg had the welcome exuberance of youth and that extraordinary touch of genius, while Kahui went about his business with such confidence and accuracy as well as an under-appreciated physical presence.
Yet none could match Kaino for all-round excellence and sustained effort. The once inconsistent Kaino was the most consistent of the lot.
"That's a credit to where he is physically," said forwards coach Steve Hansen when he was asked about Kaino's nomination as IRB Player of the Year. "He's matured into a really strong mental athlete as well. That's a reflection on why he's playing so well.
"He's always had the athletic ability to be a great player, but maybe not had the same amount of fitness as a [Kieran] Read or [Richie] McCaw, or a mental inner strength. As he's matured the mental strength has come and the desire to be the best has also come.
"At the moment you'd have to say he's the best No 6 in the world."
