As a swimmer, his countless hours of training paid off handsomely -- earning him a record 18 Olympic gold medals.
As a golfer, Michael Phelps is wondering what he's got himself into.
"It's one of the most humbling games I've tried to do in my entire life," the American tells CNN.
"I could always pick things up fairly easily, but I don't get how hitting a little object -- a little white ball, that isn't moving -- is so hard.
"Why can't I just hit this in a straight line? Or hook it, or draw it, or fade it -- I can't do it. I'm finally learning how to be able to do all that stuff and do it consistently. But I still do have some pretty bad shots."
Have a quick look online and you'll find Phelps hurling his driver away in disgust after embarrassingly topping his tee shot at the home of golf, St. Andrews in Scotland.
"Throwing clubs, using profanity -- everything comes out," Phelps says.
But there are some moments of magic, such as when -- as a 26 handicapper -- he sank a monster 150-foot putt at the Dunhill Links pro-am in Scotland last October.
However, golf requires both power and precision -- which Phelps, who was diagnosed with attention deficit disorder as a child, is slowly learning to combine.
"He's one of those players that people would look at and say, 'He has a lot of potential.' What that technically means is that the player is very long and very wild," says Tiger Woods' former coach Hank Haney, who has been tutoring Phelps in the latest series of his television show "The Haney Project."
"They never look at someone who hits it a very short distance and say, 'Oh you've got a lot of potential.' They always comment on the potential someone has as based solely on the distance of their hitting."
Haney has some history in shaping unpredictable talents, having previously worked with former basketballer Charles Barkley and boxer Sugar Ray Leonard among his celebrity TV clients.
"Michael is 6'4 but he has a 6'8 wingspan, so his arms are very long. Because of that he has a pretty long, loose swing," Haney tells CNN.
"It's capable of generating a lot of power ... That's been the biggest challenge, to get his swing better so he can control it a bit."
Haney says Phelps is "definitely getting better" after carding true hackers' scores of between 97 and 117 in six rounds immediately after the London 2012 Olympics -- where he took his career tally to a record 22 medals.
"His No. 1 goal after the Olympics was to learn how to play golf and be decent at it," Haney says.
"I think he's passionate about it. It's nice to have someone like Michael Phelps interested in the game, it's great for golf."
Golf is not only giving the 27-year-old Phelps a new hobby (if not quite a new career) -- it is also extending his commercial sell-by date.
While he's not in the $250 million league that Nike reportedly paid to sign up golf's new star Rory McIlroy, the "Baltimore Bullet" has already landed a club deal with Ping.
"Ping is a well-established global brand that should be able to deliver Phelps with huge international exposure," says British sports business expert Simon Chadwick.
"Phelps, meanwhile, provides Ping with a brand association that has a strong track-record of success at the very highest level.
"That said, this is a somewhat strange alliance that would be appear to be fraught with difficulty. It doesn't make instant sense, and quite what the tangible returns will be to both parties isn't necessarily obvious.
"If there is no expectation that Phelps will become a professional golfer, the Ping deal tends rather to imply that this is short-term opportunism -- unless, of course, the relaunch and rebranding of Phelps as a global sport or leisure brand starts here.
"If the Phelps brand in golf is to have any sustainable future, he needs to start delivering the kind of performances that fans and consumers will be looking for."