Before his loss to Nate Diaz on March 5, the legend of Conor McGregor had been built through boldness and an almost clairvoyant ability to call his own shots.

It's one thing to establish lofty standards of pay-per-view buys and fight purses as a master marketer and all-time great trash-talker. It's another if the substance of what you are inside the cage isn't quite what the hype machine made it out to be.

UFC 202: Nate Diaz-Conor McGregor II Where: T-Mobile Arena, Las Vegas

When: Saturday

TV: PPV, 10 p.m. ET

Entering his first bout with Diaz, the currency of McGregor's words had never held greater value. The cultivation of his "Mystic Mac" persona knew almost no limits.

Move up two weight classes to face a new opponent on 11 days' notice? No problem. For even McGregor's harshest of critics -- those who believed his 13-second knockout of Jose Aldo had been a fluke or still questioned what an elite wrestler with a full training camp might do to him -- there was a voice of disbelief whispering at every turn: What if McGregor is right? What if he really is as good as he says he is?

McGregor wasn't just playing with house money entering UFC 196; he was setting it on fire and laughing at the flames. And in the first round against Diaz, as he danced around the cage and bloodied his opponent's right eye with pinpoint punches, McGregor was improbably backing up just the latest in a long line of outrageous claims.

The clown prince of mixed martial arts was ready to become the sport's new king, with a pay-per-view-shattering superfight against a returning Georges St-Pierre, who was cageside, likely next on the horizon.

But McGregor's legend ran out of gas. It was picked apart, scowled at and submitted by a fighter he had taken for granted, in the face of odds the UFC's 145-pound champion had refused to accept were against him.

The two fighters will meet for a second time on Saturday, headlining UFC 202 in Las Vegas. For Diaz, who used the dramatic win (and circus atmosphere surrounding the rematch) to negotiate the kind of purse he has long deserved, the fight offers an opportunity at unlikely stardom. But for McGregor, the stakes are much higher.

There are plenty of arguments to be made how McGregor's star power could survive a second straight loss to Diaz, but his legend would never be the same. Not the one he was attempting to build entering their first bout.

That's why Saturday's rematch is a must-win for McGregor in terms of how we'll remember him down the line. It may also prove to be a must-win for the UFC.

It takes stars to drive mainstream interest, and following the UFC's recent $4 billion sale, its new owners are at a bit of a deficit in that category. It's something McGregor is well aware of, too.

"Somebody estimated my net worth to be $4 billion -- that was my reaction [to the sale]," McGregor told ESPN.com last week. "There is 95 percent bums in the game, that's the God's honest truth. Like I said, if I took myself out of here, it would be just hillbillies hugging each other to the bell. Nobody brings what I bring; nobody has done what I have done. If 2015 was McGregor bringing in all these numbers and breaking all these records and then 2016 it sold for $4 billion, I simply know my net worth now, and it's $4 billion."

When you look up and down the UFC roster, there is no one within the same area code when it comes to McGregor's value to the company as a star. Not only are Jon Jones and Brock Lesnar handcuffed by bad press and likely suspensions following their UFC 200 doping violations, it's unclear whether Ronda Rousey will ever return, let alone ever be the same.

McGregor could only increase his value to the UFC should he defeat Diaz, which by the way, would provide the company with another lottery ticket to cash whenever it pleases in the form of a trilogy fight. But a second McGregor loss would be another story.

For the most part, you only get one shot at cultivating the idea of true invincibility in combat sports. It's a false narrative, of course, especially in MMA, where one mistake at any given moment can cost you a fight. But history has proven you can earn it back by instantly fixing your one mistake, something even GSP was able to do by avenging his upset title loss to Matt Serra in 2008.

McGregor has built-in excuses he can one day lean on as a justification for the first defeat -- everything from mismanaged cardio to Diaz, the much bigger fighter, being a late replacement. But he must win the rematch decisively in order to do so. It's something not lost on the Irishman, which is why he has compounded an already stubborn decision by insisting that the rematch be contested at 170 pounds.

Dana White helped sell the UFC for $4 billion earlier this year. Ed Mulholland/Zuffa LLC/Getty Images

"What kind of fighter would I be if I said, 'Hey, I didn't get you at 170, let me try to get you at 155," McGregor told ESPN.com in June. "I'll make my adjustments. I ate up to the weight. This time, I won't do that."

In one sense, fighters are the greatest liars in all of sports, mostly out of necessity due to the irrational confidence needed just to enter the fighting arena. But McGregor never appears to be acting, even throughout the more circus-like moments in his initial rise.

That's why it's hard to imagine McGregor's confidence and boldness ever truly being the same with a second consecutive defeat to the same fighter, which history supports can be demoralizing at the elite level.

BJ Penn and Anderson Silva never fully recovered from losing their UFC titles in back-to-back defeats to Frankie Edgar and Chris Weidman, respectively. Former heavyweight champion Junior dos Santos has never been the same since two title defeats to Cain Velasquez. In boxing, both Larry Holmes (twice against Michael Spinks) and Shane Mosley (twice each to both Vernon Forrest and "Winky" Wright) never returned to the same level.

Yes, McGregor could conceivably lose to Diaz and still return to featherweight, where he remains the UFC champion. But his audacious aura -- the very foundation his star was built upon -- will be damaged.

Will McGregor one day go down as merely a talented loudmouth who was finally exposed -- twice -- for biting off more than he could chew? Or will his intangibles, skills and fighting spirit prove to be as historically significant as his ability to draw eyes?

McGregor deserves respect for how he has handled himself as a fighter, one who simply refuses to back down from a challenge. Make no mistake, he's in for another one on Saturday.

It's fitting that the fight would be in Vegas, where McGregor is essentially going all-in on himself. Considering his boldness up to this point, there should be no other way.

A victory over Diaz on Saturday is the only true way for McGregor to reclaim what was lost.