When Manny Pacquiao meets Timothy Bradley in Las Vegas on Saturday, his motivation will extend beyond avenging what he views as an erroneous defeat in their first meeting nearly two years ago.
On that June night at the MGM Grand, which also provides the setting for the rematch, Pacquiao was on the wrong end of a controversial split decision that most felt should have favoured the Filipino.
That injustice alone provides ample inspiration to overcome Bradley, but the aging WBO welterweight champion has also been stung by taunts from the American that question his desire.
"The hunger that he's looking for? It's no longer there. It's gone. It's gone. He's a tremendous fighter but I don't see it," Bradley said.
"The reason why Pacquiao really needs to win this fight is because if he loses, think about it - his career might be over."
A loss to Bradley would be Pacquiao's third defeat in four contests, a sequence broken only by November's points victory over made-to-measure Brandon Rios.
The 35-year-old stands at a crossroads knowing victory over the accomplished if unspectacular Bradley would retain his place at boxing's top table. Any other outcome and retirement beckons for a modern day great.
Even an element of doubt clouds Pacquiao's own mind, amplifying the significance of his 63rd fight, but he is confident that a career beginning in 1995 will endure beyond this weekend.
"I'm always thinking about his (Bradley's) challenge that to me that I don't have that killer instinct or hunger any more," said Pacquiao.
"So I have to prove that to him and to myself. I will show him my speed and my power.
"I feel that in my physical body that I can still fight and that's what I believe."
The importance of inflicting a first defeat on Bradley is understood by Pacquiao's trainer Freddie Roach.
"This is a 'must-win' situation and if we don't win this fight we have to maybe consider retirement," Roach said.
"So this is a big, big fight for him. Some people think we are all done and we have to prove that we are not.
"We've had a great run. I don't think that it's close to being over.
"His work ethic is great and he's training really hard and he's not missing a step anywhere.
"You're going to see us around a lot longer than you think."