"I don't have anything else that's left," the most decorated Olympian ever said Sunday in his farewell news conference in Rio.
When Michael Phelps decided to try for the Rio 2016 Olympic Games, after his short-lived retirement following the 2012 London Games, the reasoning was perfectly clear to him.
Though he managed to win six medals in London, four of them gold, he had not trained to his standards, had not been as engaged in the pursuit as he was in 2004 and 2008, when he became an Olympic legend.
In rededicating himself to one last run at glory in 2016, Phelps vowed to do it the right way. His drink-driving arrest in 2014 and the birth of his first child, son Boomer, earlier this year only reinforced that notion.
But having starred in Brazil, where he won five gold medals to take his career Olympic tally to 23, Phelps once again declared himself done with competitive swimming.
"This is it," he said at a news conference. "I said it before but this is the last time you'll see me in the water racing.
"After the relay last night, that's why I was hunched over and more emotional than I was in London, because it actually meant something. I don't want to say London didn't mean anything but this is how I wanted to finish.
"I didn't want to feel like I was forced to do something. I did this this time because I truly wanted to."
Phelps' emotional investment was evident as the meet unfolded over the past week, whether embracing young team-mate Ryan Held for breaking into tears on the medal stand or rushing to the crowd at the aquatics centre for a group hug with his son, fiancee and mother, the 31-year-old acted like a man absolutely sure of himself.
He also won six more medals, five of them gold, to validate his comeback decision from a competitive standpoint.
It is difficult to imagine any athlete challenging his medal totals - 28 overall and 23 gold - so now it is time for Phelps to find another pursuit.
The options he ran through Sunday included growing the sport of swimming, teaching more children to be water safe, and growing his family.
While there are unknowns ahead, Phelps is confident he is bowing out at the right time.
"I'm in the best place possible, with everything that's going on in my life," he added. "This is what I wanted to finish my career with. This is the cherry I wanted to put on top of the cake.
"When I decided to come back I wanted to do it the right way. I wanted to challenge myself, see how much more I could actually do. Looking back at the two-plus years spent training, I don't have anything else that's left."