Nicky Hayden has admitted he is confused by his former team-mate Casey Stoner's decision to retire from MotoGP.
Reigning world champion Stoner announced in May that 2012 would be his last season in the sport.
That means he will walk away at the age of 27, after just seven years in MotoGP - although in that time he has won two titles and 37 races to date.
Hayden was paired with Stoner at Ducati in 2009 and '10 before the Australian left for Honda, where he won the championship at the first attempt
"I'm a little bit surprised, but Casey does things his way," Hayden told the Australian Motorcycle Grand Prix's podcast.
"I'm just surprised because to be winning, to be on top, to have a team like that behind you, it seems like life would be pretty good.
"So I don't understand why he would [retire], but that's his decision and I respect it.
"He's given a lot to this sport. Casey, like him or not, it's not like he rode around and milked it. When he's on the track, he's given a lot. So I say he earned the right to do what he wants.
"I think it's a pretty good life going around the world riding these motorcycles, so it seems strange, but it's his decision.
"He probably doesn't understand why I want to keep doing it..."
Hayden recently extended his Ducati contract into a fifth year.
The 31-year-old has not won a race since his title-winning campaign with Honda in 2006, but still believes he can return to the top before he retires.
"I've been at Ducati now a couple of years and had some OK results, but I think my best Ducati years are ahead of me," Hayden insisted.
"We've had a couple of not great years but there's no reason why this team and this bike can't win.
"We have the resources, we have the sponsors, and they've won before. People forget - it wasn't that long ago that Ducati was winning races, and I believe it's very possible."