Tiger Woods' former caddy said he once had to pull over on the side of a highway because Woods was determined to practice his swing

• Tiger Woods once made his caddy pull over on the side of the highway so he could practice his swing.
• His former caddy Steve Williams said no other golfer was as driven and obsessive about improving as Woods.
• Woods' obsession with his swing and perfection has been well-chronicled, with some thinking it had a negative effect on him.

Tiger Woods' insatiable work ethic and desire to improve can strike at any time and any place.

Woods' former caddy Steve Williams said in the HBO documentary "Tiger" that Woods once made him pull over on the side of a busy highway so he could tinker with his swing.

"We were driving down this freeway, and he goes, 'Stevie, stop the car. Stop the car.'" Williams said. "He got the golf club out of the trunk, and he's swinging on the side of the road. Here's Tiger Woods on the side of the freeway in Toronto, swinging a golf club.

"He's got this thought in his head, 'If I can just do this,' and he couldn't wait until the next day or until he got back to the hotel or wherever it was. It had to be now. There's nobody that would do that."

Woods' swing has always been a point of obsession for him. He famously changed it several times throughout his career, even at the height of his prowess.

"He always believed he could get better, and he could strive for perfection," Williams said.

Of course, Woods' obsession with golf also had its downside. In "Tiger," Woods' high-school girlfriend Dina Parr said she was worried that Woods' parents, who famously pushed Woods toward golf superstardom, were building a "robot" and not teaching him life skills.

As an adult, his days often consisted of practicing, working out, and then playing sports.

"I used to get up in the morning, run 4 miles. Then I'd go to the gym, do my lift. Then I'd hit balls for two to three hours. I'd go play, come back, work on my short game. I'd go run another 4 more miles, and then if anyone wanted to play basketball or tennis, I would go play basketball or tennis," Woods told reporters in 2018. "That was a daily routine."

In "Tiger," author Robert Lusetich said he used to ask Woods why he kept changing his swing, saying he was already playing the best golf ever.

Woods responded: "You always ask me that. I'm going to be way better than I am now."

"Tiger" airs on HBO on January 10 at 9 p.m. ET.