The brightest stars burn out the fastest - just look at Russell Westbrook. If you only know how to drive in top gear, what do you do when your top gear runs out? It's not like there aren't signs of aging; there always are. But these guys don't accept the concept of taking it easy. Doc Rivers learned that with Kevin Garnett.
Later in KG's career, Doc started to manage his workload. Most players would accept playing fewer regular-season minutes, skipping a few games. Not KG; he couldn't accept Doc sitting him during practice.
“I can't sit out practice; they'll see me. It's a weakness; they think I'm getting old. Don't do this to me, coach; I gotta play.”
Kevin Garnett, The BS Podcast
Doc explained to KG he has bad knees, and he's not letting him practice. He sent Garnett to the sidelines to watch practice and brought Leon Powe into his spot. This is where KG's top gear started working.
“He's watching them, and they're working out, and he starts mimicking everything Leon Powe does. He's on the sideline, and Leon Powe is running down the court. He starts running down the court pretending he's doing the same things. So when Leon Powe is setting a screen, he's setting a screen on an imaginary person on the sideline. Leon Powe gets a rebound; he jumps up and gets the rebound. Leon Powe runs down, and he's beating Leon Powe down the sideline. Doc's yelling at him, 'Stop it, cut it out!! I'm gonna have to stop practice!!' Garnett's ignoring him, and finally, Doc has to blow the whistle and end practice.”
Jackie MacMullan, The BS Podcast
Doc wasn't the only coach that had to deal with this. Flip Saunders would have a walkthrough about the opposing team's offense, simulating their plays. But every time the ball would come close to KG, he'd break out the play. Then Flip would tell KG to cut it out because that's not the point of the walkthrough. The next time the ball came close to KG? Same thing.
The modern, analytics/sports science based approach would call all those jumps, cuts, and all-out plays stupid. Today's NBA is focused on optimizing the future and often forgets the present and the past. Without that attitude and intensity, KG wouldn't have been the final piece of a Championship mosaic.
You can't just turn off a habit or an attitude you've cultivated for over a decade, particularly when that attitude was the foundation of your success. For some guys, that's the only way they know how to play.