You learn a lot about a man from the way he responds to adversity. To his credit and to his detriment, Floyd Mayweather spent most of his boxing career not letting us learn much about him.

Then came Round Two against Sugar Shane Mosley. Mayweather got rocked like never before by a right hand. He survived the crisis—only to get rocked again, much harder than the first time. His knees dipped. He had to hold. But he never touched down, and he got through it.

And the way he responded in Round Three was, seemingly, a revelation. Mayweather didn’t go into a defensive shell, didn’t look to run and potshot his way to a points win. He took the fight to Mosley. He backed up the man who, just a couple of minutes earlier, was possibly just a punch or two away from knocking him out. Mayweather faced adversity and he fought magnificently—the operative word being “fought.” He had come through the worst moment of his career shining more brightly than ever before.

What a difference a year makes, huh?

Today—Sunday, May 1—marks one full year since the Mosley fight, and one full year of inactivity for Mayweather. This week, Mayweather’s name will be removed from The Ring magazine’s and ESPN.com’s rankings, both of which follow a rule that if you haven’t fought for a year and don’t have an upcoming bout scheduled, you join the ranks of the unranked (unless there’s some unique, extenuating circumstance).

Mayweather shows no particular desire to be a professional boxer. He could have made $40-million or more to face Manny Pacquiao at various times over the past year or so but, as best we can gather, didn’t have much interest in the gig.

If you believe what the IRS has to say, a paycheck that size could come in handy for the man who likes to call himself “Money.” So why isn’t Mayweather at least considering it? Why has he gone a full year without fighting? Why is the possibility of a Pacquiao fight so dead at this moment that promoter Bob Arum is already making overtures to Juan Manuel Marquez for a fall fight with Pac-Man instead?

Some have theorized that Mayweather is just waiting out his legal situation before doing anything. I’m not buying it; he was balking at the Pacquiao fight last summer before his legal situation had reached significant proportions.

Here’s a more wilder, crazier, but at the same time perhaps much more accurate, theory for why Mayweather let himself go a year without boxing: because those right hands from Mosley ruined him. Floyd was able to shake them off in the moment. But he wasn’t able to shake them off after the moment had passed.

Phrased another way, against Shane Mosley, Mayweather had his Hector-Camacho-vs.-Edwin-Rosario moment. Except unlike Camacho, Mayweather didn’t start running DURING fights; he started running FROM fights.

To refresh your memory, “Macho” Camacho was an unbeaten rising star, climbing the pound-for-pound lists, when in 1986 he fought veteran puncher Rosario. In the fifth round, Camacho was badly hurt by an overhand-right/left-hook combination. He survived the round and spent the next several on his toes—moving, jabbing, stinking it out but winning rounds. Then he got drilled with another left hook in the 11th, and it was all he could do to make it to the final bell. Camacho won a split decision.

Sports Illustrated’s Pat Putnam wrote that after the fight, then-seven-year-old Hector Camacho Jr. told his old man, “Daddy, you are lucky you’re alive.” The next morning, Camacho admitted to his girlfriend, “Hey, if this is macho, I don’t want no part of it.”

So Camacho never fought macho again. He fought ugly whenever possible, developing into possibly the least entertaining and most underachieving fighter of his generation.

Hmm. Not entertaining. Underachieving. Sound like anyone we know?

For all of his life, maybe Mayweather really bought into his “greatest of all-time” nonsense. Maybe he truly took his unbeaten record to mean that he couldn’t be beaten. If so, that second round with Mosley rocked his world, blew up everything he thought he knew. Hey, guys get hit, guys get hurt, and Mayweather showed a pretty good chin and plenty of heart. But he was reminded that, for all of his boxing talent, he is human. He can be separated from his senses if the right punch lands in the right spot. And he didn’t like that feeling. He decided it was something he never wanted to feel again.

It’s like that old refrain about how there’s only one surefire form of birth control. If Mayweather wants to be absolutely certain he’ll never get hurt from a punch, he has to abstain from boxing.

Mayweather is only peripherally involved in the sport at this time. He doesn’t engage in boxing-related interviews, and he rarely attends the fights. When he did make a ringside appearance at the Victor Ortiz-Andre Berto fight two weeks ago, he heard vociferous booing and chants of “Fight Manny” from the Foxwoods crowd whenever he was shown on the big screen. What did Mayweather do? He flashed the widest smile he could. Many of us fall back on a sense of humor as a defense mechanism. Based on the evidence brought to us courtesy of UStream, it’s safe to say Mayweather doesn’t have a very good sense of humor. So his smile is his defense mechanism. You think he’s happy that fans are booing him and calling him a coward? Of course not. But he’s not going to swallow hard and sulk. Instead, the smile comes out.

The rankings show that Floyd Mayweather is not an active fighter anymore. Deep down, he seems to believe he’s not a fighter at all anymore. Yes, he’d been burning out on boxing for the last four years or so. But something flipped a switch, made him transition from part-time boxer to full-time celebrity sports bettor.

That something was Mosley’s right hand. Mosley is fighting Pacquiao for an eight-figure payday this weekend. Mayweather hasn’t fought anyone since taking on Sugar Shane. On that night, Mayweather had his hand raised. But Mosley can take credit for it if that hand never gets raised again.

Eric Raskin can be contacted at RaskinBoxing@yahoo.com. You can follow him on Twitter @EricRaskin and listen to new episodes of his podcast, Ring Theory, at http://ringtheory.podbean.com.