Money makes the world go.
The Stockton native would be the first one to tell you, he's not in this sport to make friends or get famous; he just wants to get paid.
That's why he contemplated a switch to professional boxing, where the payouts are far more lucrative at the top of the card then they are fighting in MMA, even if it's with the largest organization in the world, the UFC.
In fact, Diaz had a deal in place for a boxing match that would have earned him a handsome penny. But he ultimately turned it down for an exclusive eight-fight UFC contract and an immediate title shot against Georges St. Pierre.
But then it all went south.
After agreeing to the contract and getting a main event pay-per-view slot opposite one of the pound-for-pound greatest fighters on Earth, Diaz went awol.
He retreated into the deep recesses of Stockton, California to train his mind and body for the challenge that was to come. It's what he does, after all. Train, eat, sleep; train, eat, sleep.
But when it came time to do some promoting and show up to a pair of press conferences in Canada and Las Vegas, he failed to show up. This so angered UFC President Dana White that the decision was made to take Diaz out of his title shot and off the card altogether.
There were even a few hints that he would be cut from the promotion altogether.
That quickly went to the wayside, however, when Diaz found himself staring at a contract to fight B.J. Penn, who had also just lost his opponent, Carlos Condit, thanks to Diaz. Both men signed on the dotted line and here we are.
Now, after all that, regret is rearing its ugly head.
As Diaz explained at the open media workouts (via USA Today), if he could take it all back now, he would stick with boxing and leave MMA behind ... for the time being:
"If I had my chance to do it over again, I would have gone back to the boxing contract. It would have paid me more money. ... Later on, I'm sure they would have had me back here."
Indeed, speculation has Diaz losing out on at least six -- and maybe seven -- figures for missing out on fighting St. Pierre in the main event of a major pay-per-view over the Halloween weekend.
That's quite a bit of coin, folks.
When it comes to Diaz, it's always about how he can get the most buck for his bang. The how, the where and the who are nearly irrelevant.
He's in a tough situation now, though. If he loses to Penn on Saturday at the Mandalay Bay Events Center in Las Vegas, Nevada, he'll be multiple fights away from regaining a title shot and there's nothing to say St. Pierre will remain champion during that time.
In short, a lot more potential cash will disappear once again.
On top of that, his contract with UFC is exclusive, unlike the deal he had in place with Strikeforce. Even if he wants to go to boxing now to augment is Octagon salary, it's no longer an option.
Maybe that's not such a bad thing. Maybe that very fact will provide all the motivation he needs to emerge victorious when he gets down and dirty inside the cage with "The Prodigy."
Cash is king.