The French believe the vines must struggle if they are to produce good wines.

Friedrich Nietzsche reckoned that anything that didn't kill him made him stronger and Graham Henry used to talk about the power of defeat as a more useful learning tool than victory.

These are all variations of a theme - that adversity can be an invaluable part of the mix when it comes to achieving greatness.

That's often forgotten in New Zealand rugby circles, as the greats of today have largely enjoyed unblemished careers.

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Collectively, Richie McCaw and Dan Carter have known failure - part of All Black sides that have bombed at World Cups. But individually, neither has known a prolonged period of disappointment.

They have never been dropped, never known their form to collapse or flaws to blight their game.

Those clean lines of achievement, those neat rows of perfect rugby games, sit in the sub-conscious as the ideal career path. Those players whose careers haven't travelled the same immaculate route somehow don't carry the same appeal - and yet they should.

Adversity is perhaps the secret ingredient in the recently selected All Black wider training squad.

There are plenty who have had to struggle, who have been stung by rejection, felt the cold blade of the selectors or had parts of their game melt down without reason.

Those who have lost it, know just how much they want it.

Those who have to battle have already shown a mental resilience that will serve them well in an arena that will be relentlessly hostile.

One of the more interesting salvation stories is that of Hurricanes wing Julian Savea. There is no kind way of describing his form last season - he was awful. He was a liability under the high ball, not much chop at catching any ball for that matter, and there was no discernible evidence as to how on earth he was named IRB World Junior Player of the Year in 2010.

His turnaround this year has been phenomenal. His security on defence has been outstanding. His aerial work among the best in the country and one-on-one, he's left defenders stranded or sent them sprawling. He's a different player and his recovery is down mostly to hard work, smarter work and a more inclusive culture at the Hurricanes where he's felt more comfortable with his role.

Tenacity, perseverance and commitment weren't necessarily foundation values for Savea before this year - but they are now and the horror of 2011 lives with him, drives him and may make him a surprise star of the June series.

"He's a big guy with a lot of pace and scores lots of tries. On form, we thought he was the guy to pick," said All Black coach Steve Hansen about Savea. Interestingly, the man competing directly against Savea for the All Black No 11 jersey knows plenty about adversity. Zac Guildford has battled his demons since making the All Blacks in 2009.

He suffered the most public humiliation late last year when his world collapsed during a booze-filled day of carnage in Rarotonga where he ended up in a bar naked and bleeding.

His strength of character since has been impressive. Since his spectacular fall from grace, he's attended counselling and kicked the booze. His form has slowly improved throughout the campaign, with promising signs he was back to his best against the Blues.

"I knew if I worked hard, kept out of trouble and did the right things on the field, then eventually it would come, and I'm very grateful to have the opportunity again," Guildford said when he was called up as a replacement for the injured Richard Kahui.

Hika Elliot could add to the team of resurrection men if he's called up in place of Keven Mealamu. Like Guildford, Elliot has had issues off the field - been involved in alcohol-related incidents that have reflected badly on him.

"When I first made the All Blacks, I was still quite young and I didn't grasp the concept that being an All Black was 24/7," he told NZ Rugby World in 2011. "We have to do our growing up in the public office and in some instances I didn't live up to that [expectation] of good behaviour."

He has been shaped by those dark times, learned how to control the intensity of his emotions and emerged a stronger, better person.

The list of rebuilt personalities goes on: Aaron Cruden, who had to recover from testicular cancer and then the most galling dropping in many years after his first test start went off track in 2010.

Ma'a Nonu has been dropped at World Cups and from World Cups and sacked by the Hurricanes.

Piri Weepu has been dropped from a World Cup squad and had his diet and conditioning regime questioned by a nation. Ali Williams endured two years out the game with a damaged Achilles.

There is a natural instinct to think of some of these players as broken goods. But that's the point - they are not. They can be improved, strengthened and bettered by having been broken. The qualities they show to recover are qualities that will be invaluable when the pressure comes on.