"I think he was humbled a little bit," Cuban said Tuesday during an appearance on 1310 The Ticket in Dallas. "I think he didn't like being called out for his weight and other things, and it finally clicked that there's a level of discipline that's required.
"All athletes at his level go through it at some level, where things are just easy and you're always used to being the best and you're always used to getting all the accolades. Then when something doesn't go according to expected, it makes you reconsider."
Doncic acknowledged in early December that his conditioning needed to "get back on track," saying he relaxed "maybe too much" in the weeks between Slovenia's Olympic run and reporting to Dallas for training camp. Sources told ESPN that Doncic reported to camp weighing more than 260 pounds for the second consecutive year.
Doncic has since dropped more than 15 pounds, according to sources, to get close to his rookie weight.
Not coincidentally, he has returned to All-NBA form after a relatively slow start to the season.
In his first 21 games of the season, Doncic averaged 25.6 points, 8 rebounds and 8.5 assists with a minus-5.5 net rating, proof of his lackluster defensive performance. He then rested three weeks to recover from a sprained right ankle that he had aggravated multiple times and worked on his conditioning.
In the 23 games since the layoff, Doncic has averaged 29.3 points, 10.3 rebounds and 9.4 assists with a plus-13 net rating, evidence of his drastic defensive improvement. A two-time first-team All-NBA selection who just played in his third All-Star Game, Doncic has averaged 35.4 points, 10.3 rebounds and 9.8 assists in 10 games since it was revealed that he received zero media votes to be an All-Star starter.
"He knows what he needs to do, and it finally clicked that if he's going to be the best -- and I know he wants to be the best -- that there's certain things he has to control," Cuban said. "Once he got a handle on those things, it's just been 'Katie, bar the door.' He's just been unstoppable."