Instead of sleeping in during a beautiful morning in Los Angeles, Tatum completed an hourlong on-court workout. He didn’t mirror the preparation intensity needed for a playoff game. Nor should he. Yet, Tatum still obsessed over his footwork, post-up moves and finishes as if those small details could make a big difference in the Celtics’ quest to defend their NBA title. “I just try to get better every year,” Tatum said. “There’s a lot of things I want to accomplish. There’s a lot of things I want to do. And there’s so much more to get better at. So I’m just approaching it with that mindset.”