For Jerome Kaino, the process of proving himself is relentless. In his early All Black years it was about proving to himself he was good enough to be there.
Once he was established it was about proving to his peers that he was good enough to stay there and when he came back from Japan this year, it was about proving that he still had what it took to play test rugby.
He'll win his 50th cap tomorrow night and while it won't be at the forefront of his mind, Kaino knows he and Liam Messam will be on trial.
All Black coach Steve Hansen has said that Kieran Read will start next week in Hamilton.
Kaino will have to vacate the No8 jersey and then what?
"I think me and my old mate Liam Messam are going to have butt heads sooner or later," says Kaino.
"I think that's the go once Kieran comes back in. We always talk about how we can improve each other's game. It just comes down to the coach's preference. We play a similar style. He's a little bit quicker and more agile but it comes down to the opportunities that we get and how we take them."
Having maybe struggled to understand the ruthless and unforgiving nature of test rugby earlier in his career, Kaino will hardly have to have the importance of this test explained to him.
There's the balance of the series, the need to inflict some psychological damage on a fast-improving England team with an eye to the World Cup.
Kaino also knows he'll be on the bench or in the stands next week if he doesn't nail his performance.
And he most definitely didn't terminate his lucrative stint in Japan to give most, but not all of himself.
About this time last year he just couldn't stand it any more - he was watching a superb All Black team from afar and he knew, because every fibre in his body told him, that he wanted to be part of it.
"I missed it a lot," he said. "It was awesome watching them go undefeated, but deep down inside I really wanted to be a part of this group and come home and play again.
"I want to be judged on my actions now and I wanted to earn my place in the Blues and the All Blacks and not just off my reputation.
"It was late July last year around the Rugby Championship [that I really felt I wanted to come back]. I had spoken to Steve Hansen and John Kirwan and they said if you come back and play well, we will play you.
"I backed my ability to come back and play well, and that was all the motivation I needed to come home."