Michael Phelps kept his word after swimming into history with one last, immense Olympic appearance on Saturday.
The greatest Olympic swimmer, and to many the greatest athlete as well, called time on his sensational career with an 18th gold medal and the recognition that he had done everything he had set out to do.
Asked why he had to go, when he was still so obviously a winner, still dominant and able to perform, the 27-year-old American referred the questioner back to something he had promised himself long ago.
"I told myself I never want to swim when I'm 30," he said.
"No offence to those people who are 30, but that is something that I always said to myself. That will be in three years and I just don't want to swim for another three years.
"And I've been able to do everything I wanted. I've been able to put my mind to the goals that I wanted to achieve and (coach) Bob (Bowman) and I have somehow managed to do every single thing.
"I think if you can say that about your career, there's no need to move forward. Time for other things."
Phelps will leave London with 22 Olympic medals from three Games, having competed in four in total, including a record haul of eight from Beijing.
His rivals will miss him, the American providing a benchmark for their own achievements, but he had no regrets about departing.
He has kept a journal all year, finding plane journeys a particularly good opportunity to let his mind take flight, and he said his entry for Saturday would be simple.
"I can probably sum it up in a couple of words and just say 'I did it'," he stated.
"That's pretty much all I can say. Through the ups and downs, through my career, I've still been able to do everything I've ever wanted to accomplish. I've been able to do things that nobody else has ever done.
"The memories that I've had from this week will never go away. Soon enough they'll be on a piece of paper, in my journal, and I'll have them written forever."
Phelps started his Olympic journey at the Sydney Games in 2000, as a 15-year-old. He has travelled to Athens, Beijing and now London - as well as numerous world championships - to amass an astonishing collection of medals.
Now, he said, he would travel for fun.
"I want to travel a bunch. I have been able to see so many places around the world, but I have never been able to experience them," he said.
"Whether it is travelling through Europe, or going back to Australia, or South Africa - something (South African swimmer) Chad (Le Clos)and I were talking about.
"The competitive side of my career is over, but there are things I would like to do around the sport - working with my foundation is very important to me. Also my swim schools, teaching kids how to swim. I just want to have fun."
Earlier in the week, Phelps had described how he was flagging up each race in the ready room as his last 100 butterfly, his last semi-final, his last individual final, and ticking off a list.
He has said he expected the full force of what he had done, and what he was leaving, to hit him emotionally once it was all over.
There were tears in his eyes, and a wobble of a pursed lip, on the podium as his mother and family watched on from the stands.
"As soon as I stood on the podium I could feel the tears start coming," he said.
"I tried to fight it, but then I decided to let go. I'm just going to take these last couple of moments, of memories of my career."