There's a constant tug inside the best boxers, a challenge they hear from fans, reporters or themselves.
But the November 2009 challenge against welterweight world champion Miguel Cotto? Now that's a test, a fight-of-the-year-caliber challenge against a true 147-pounder with major-league skill.
That's why Pacquiao told The Times the Cotto victory is his third greatest fight.
Puerto Rico's Cotto was a year removed from what was then his only defeat, a beating by Antonio Margarito deserving of an asterisk when plaster-caked hand wraps were confiscated from Margarito's gloves months later, before his loss to Shane Mosley at Staples Center.
Before Cotto fought Pacquiao, a photo emerged showing Margarito celebrating the Cotto win while wearing handwraps that were stained in the same area over the knuckle where the Mosley wraps were stained.
"I know about the photo," Cotto told The Times, leaving it at that.
Cotto, a world champion since 2004 who built his reputation by pummeling foes with well-aimed body punches, rallied from the Margarito loss with two victories, including a welterweight-title triumph over Joshua Clottey.
The proud, reserved champion landed an early head shot at Pacquiao in the first round and kept the Filipino at a distance until late in the second round, when Pacquiao moved in to deliver a three-punch combination.
In the third, Cotto threw a left that Pacquiao sidestepped while touching Cotto enough to merit a knockdown ruling from referee Kenny Bayless after Cotto went to the canvas on one knee.
There was no mistaking Pacquiao's true knockdown in the fourth. He sent a hard left to Cotto's chin late in the round, cutting the champion below one eye.
Cotto couldn't keep up in the toe-to-toe exchanges, and Pacquiao was too fast to allow Cotto to punish him to the body as he'd do to others, and by the ninth round Cotto was bleeding from his nose into his mouth.
Pacquiao was battering Cotto so often by the 11th that the Puerto Rican, bleeding at the left eye, could only muster jabs.
Swollen under both eyes, and blood gushing from his left, Cotto took some more punishment in the first seconds of the 12th and Bayless decided that was enough, stopping the fight 55 seconds into the round.
The former flyweight Pacquiao was a true welterweight champion.
Cotto, meanwhile, moved on to get a 2012 date with Mayweather that he lost, but recovered to claim a middleweight title last summer in New York, beating Sergio Martinez.