Tiger Woods has gone through a few different swing changes in his time, and when golf fans analyze them, they tend to focus on the more recent ones: his work under Hank Haney, for instance, or Sean Foley in 2013.

Along the way, it’s easy to gloss over what a gutsy call a young Woods made in 1998, when after winning back-to-back-to-back U.S. Junior Ams, followed by back-to-back-to-back U.S. Amateurs, followed by the 1997 Masters victory by 12 shots, he decided to embark on a sizable swing change under the tutelage of Butch Harmon, Golf Digest’s No. 1-ranked teacher.

The biggest issue, as Woods explained in his cover story from the September 2000 edition of Golf Digest, was his lower body moving out of sync with his arms. (You can see that and the rest of our Golf Digest archive right here. If you’re a golf nerd like me, you’ll love it).

“One of the problems I had when I first turned pro was getting in a ‘stuck’ position on the downswing,” Tiger explains. “The club would get behind me, and I would then have to try to square it at impact with my hands. Sometimes I could, other times I couldn’t, and the ball would fly anywhere.”

To fix it, Butch and Tiger focused on Tiger’s first move down from the top of his backswing, Woods goes on to explain. He wanted to engrain the feeling of “letting his arms fall as my weight transfers to his left side,” which would keep his arms in front of him before swinging them through.

To do that, Tiger said in his famed Golf Channel Academy Live video below that Butch would have him perform a simple drill: taking the club up to the top of his swing, come to a full stop, and then swing through.

“This is a drill he’d make me do for hours upon hours, I’d be out there sweating in 100 degrees,” he said. “I couldn’t stand it. I still can’t stand it. I hated doing it, but I knew it was something I needed to do in order to feel where I wanted to put my arms.”

He may have hated it, but needless to say, it worked. When Tiger grooved his new swing, he went on a heroic run that led to the best golf of his career and, of course, the Tiger Slam. It wasn’t easy, but if nothing else, it was worth it.