James Harden may have been traded to the Brooklyn Nets, but several contenders around the NBA considered making the move themselves. One such team, the Miami Heat, reportedly dropped out of the proceedings fairly early. In fact, multiple reports claimed that they decided not to trade for Harden before the season even began.
There are a number of valid possible explanations for that decision. The Heat just made the Finals. The young players that the Houston Rockets would've wanted in a deal were a big part of that surprise run, and Miami easily could've preferred keeping them to pursuing a veteran star. But Udonis Haslem has another theory. He implied on the Complex Sports Podcast that Harden's partying was the reason why he wouldn't have been a fit with the Heat, saying "you can't bring James Harden to Miami."
Haslem, who largely doesn't play but has retained a roster spot as a veteran mentor and pseudo-assistant coach, joked that he "would've aged 15 years trying to be his OG."
Harden is known for his partying habits even in an NBA filled with players that like a good time. He missed the early portion of training camp in Houston because he was partying across the country, and in a city with as much nightlife as Miami, he likely would've continued on that path in a way that the Heat organization tends not to appreciate.
While Miami may be a party town, the Heat are decidedly not a party organization. Pat Riley has built an organizational infrastructure on fitness, discipline and accountability. Heat players are regularly tested for body fat percentage and endure lengthy in-season practices that most teams eschew. It takes a certain type of mindset to thrive with the Heat. Jimmy Butler has it. It's entirely possible that the Heat simply decided that Harden doesn't and that's why they decided not to go all-in on acquiring him.