A hamstring injury sustained two weeks before the 2012 Games forced Merritt to drop out of his heat in London and cost him the chance of defending the 400 metres title he had won four years earlier in Beijing.
In 2010, what he described as the "foolish, immature and egotistical" decision to take a penis enhancement product that turned out to contain a banned steroid earned him a 21-month doping ban.
But the incident that taught him the lesson most painfully came when he was just 13 years old and his brother Antwan died after falling out of a dorm room window while attending college.
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That accident has driven Merritt not only to make the most of his considerable talents on the track but also to ensure he secures his future once he hangs up his spikes.
"My brother wanted to do a lot of things and can't do anything because he's not here physically," Merritt said at a U.S. Olympic Committee event in Beverly Hills, California earlier this year.
"So I want to maximise what I can do now to set myself up for the next chapter of my life.
"I don't want to be an Olympic gold medalist and broke. That happens in the U.S. a lot."
To that end, he has already started up a trucking company and is looking into opening a series of childcare centres.
His first priority next month, though, will be the business of getting around one lap of the track faster than anyone else.
STATEMENT TO RIVALS
The 30-year-old, who also won 4x400 Olympic relay gold in 2008, qualified for the Games when he stormed off the final bend at the U.S. trials to win in 43.97 seconds, the only sub-44-second time in the world this year.
It was a statement that will have been noticed by his main rivals, reigning Olympic champion Kirani James and Wayde Van Niekerk, whose barnstorming run of 43.48 seconds earned him a first world title in Beijing last year.
The unrelenting pace of that race, which Merritt started strongly only to be overhauled by the South African and finish second in 43.65 seconds, has convinced the American of the need to tweak his approach to the 400 metres.
"You have to be able to be out in front and still be able to hammer," he said.
"Being out in front and still pushing it, pushing it, is just different. And that takes mental training."
The Virginia native did not grow up dreaming of becoming a track star and took up running only because his high school football coach insisted on it.
"My coach (in) my junior year said, 'I need someone to run the 400'," Merritt, who now lives in Orlando, recalled.
"I said, 'I'll run it'. And I ran it and I won. And I kept running."
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