As Joe Calzaghe prepares for perhaps the biggest fight of his career against Mikkel Kessler, the 10-year WBO super middleweight champion says that he needs such challenges to bring out his best.
Here's a look at six of the greatest tests the Newbridge man has faced in the ring - and how he has risen to the task on each occasion.
After three years as a professional, Calzaghe had won all 16 of his fights, had only gone beyond the fourth round twice, and only been taken the distance once.
But there was a distinct sense that he was thrown into the lions den for this, the first defence of his British title.
West Ham's Delaney was a talented 24-year-old who had won all 21 of his bouts.
To Calzaghe's chagrin, the Welshman's then-promoter Mickey Duff lost the purse bid, meaning the bout would take place on hostile territory, in Brentwood, Essex.
Two thousand fervent Delaney fans packed the International Centre, but their anti-Welsh jibes served to pump up Calzaghe.
After just 20 seconds Delaney was dropped for the first time in his career, and his nose was broken following a second first-round knock down.
The Englishman battled on, but was stopped after two more knock downs in the fifth round.
Eighteen months and five easy wins after Delaney, Calzaghe faced the fight he still considers his hardest.
The Welshman had been due to challenge Steve Collins for the WBO title, but his retirement meant former champion Chris Eubank stepped in to contest the vacant belt at the Sheffield Arena.
Eubank was past his best and struggled to make the weight at short notice, but the old warrior lived up to his promise to take the young challenger "into the trenches".
An adrenaline-fuelled Calzaghe made a spectacular start, a huge shot dropping his opponent in the first round for the first time in his life.
But the Welshman's inexperience meant he wasted too much energy in his early onslaught, Eubank rallying and forcing his foe to show champion qualities.
Calzaghe dug deep to go the 12 rounds for the first time in his career, and - despite a large points advantage - he was still trading blow-for-blow as the bell ended a simply spectacular fight.
Calzaghe's first five defences saw a sharp decline in the quality of his work, and after a controversial split-decision win over Robin Reid the points victories over Rick Thornberry and David Starie were two of the worst of his career.
While Calzaghe blamed an elbow problem that stopped his sparring and left his timing off, the Americans - ever mistrustful of European fighters - only saw a champion there for the taking.
Across the Atlantic, Omar Sheika was seen as the future of the super middleweight division - and he was not shy of telling the world that he would "kill" the champion when they met at the Wembley Conference Centre.
But Calzaghe suddenly found himself injury free, a development he attributes to the fact that he gave up playing golf.
In training camp he was able to do his first sparring for a year, and quickly recovered his timing and form.
Sheika's comments wound up the Welshman, and he manhandled the challenger from the opening moments.
The American was blown away by a classy, physically dominant performance from Calzaghe, who wildly celebrated the relaunch of his career after the fifth-round stoppage.
Impressive defences against Richie Woodhall, Mario Veit and the hapless Will McIntyre maintained the interest of the US audience, paving the way for a big-money match-up against the former IBF champion from Philadelphia, Charles Brewer.
"He was a tremendous fighter," said Calzaghe. "He lost his title to Sven Ottke, but that was a bad decision and I know he came here convinced he would win."
Brewer - a converted southpaw who carried a very hard left - had a reputation as a brawler, and Calzaghe knew his best chance of winning was to box.
But the champion was caught to the body early on, and a combination of adrenaline and the fervent Cardiff International Arena crowd drew him into a toe-to-war war.
"I can rarely resist if my opponent is up for it," admits the Welshman.
Calzaghe was on top, but he was stunned by a superb Brewer combination in the seventh.
After being berated in the corner by father and trainer Enzo Calzaghe, the champion turned to his boxing skills for the rest of the fight to close out a comfortable points decision.
"It was one of my best fights and one of the most exciting for my fans," said Calzaghe.
A laboured win over Miguel Jimenez and a KO of the farcical Tocker Pudwill followed Brewer, and Calzaghe admitted to feeling "frustrated and complacent".
That was a dangerous combination, as next up at the Cardiff International Arena was the 'Slama from 'Bama, Byron Mitchell.
The former WBA champion arrived in Wales as very much a live contender - strong, in shape, and with huge power in both fists.
Again, Calzaghe's obvious path to victory was to box and move... but again the champion got caught up by the occasion and dragged into a slug-fest.
The Welshman tore into his foe in a spectacular opening, but while he landed with his wild, looping shots, Mitchell's less-showy work was straight, accurate and damaging.
The pattern continued in the second round as Mitchell caught his foe with three body shots and a short, hard right.
The champion spun round and dropped to the floor for the first time in his life, as a gasp preceded stunned silence in the CIA.
Calzaghe cleared his head and resolved to go straight back to war, evading Mitchell's killer blows before blasting him to the floor with a left hook.
The champion never gave his dangerous foe the chance to recover, leaping on him and forcing a stoppage with a furious attack, prompting one US commentator to describe "a second round straight out of Hollywood".
With the boxing world again at his feet after the Mitchell mauling, Calzaghe contrived to take it on his shin and see it dribble away.
A series of uninspiring opponents, renewed injury worries and a messy divorce led many to believe that the champion was over the hill and ready to be taken by the new US super middleweight hope, Jeff Lacy.
The hype surrounding Lacy - the "mini Mike Tyson" - was infectious. "Ruthless", "devastating" and the "saviour of boxing" were some of the milder plaudits lauded on the St Petersburg man.
The pre-fight wisdom was that Calzaghe had to stay away from the challenger, to be wary of the power that had dismantled Reid and stopped 17 of 22 opponents.
Instead, he went straight into close-quarter combat, his hand speed allowing him to land furious clusters of punches while Lacy's increasingly scrambled brain was still getting his shoulder muscles into gear.
After 12 rounds of total dominance and supreme sporting skill, Lacy's own promoter Gary Shaw was screaming for the fight to be halted, and only a delay for loose tape on a glove saved the challenger from a stoppage.
The last word goes to boxing legend Sugar Ray Leonard, who admitted to knowing little of Calzaghe before the fight.
"Within two rounds I was a Calzaghe supporter, I stood up in front of the TV shouting, 'Wow, look at this guy'!" said Leonard.
"The performance he produced was amazing. It was Joe's great accomplishment, to reach that level, to scale that peak."