From Michael Jordan to Usain Bolt, a select few elite athletes have attempted the switch to another top-level sport in a trait psychologists see as a "high need to achieve" coupled with filling a gulf in their lives.
Sprint king Bolt is the latest example, with the eight-time Olympic champion on a mission to become a professional footballer, trying out with Australian team Central Coast Mariners after retiring from track and field.
It is a boyhood dream for the 32-year-old Jamaican, who remains the 100m world record holder. But his abilities have been questioned, with the fitness levels and skill-sets needed for soccer very different from being the fastest man on earth.
Martin Hagger, a world-renowned psychologist at Curtin University in Perth, said sports-hopping at the end of athletes' careers was never easy.
"Athletes like Bolt have what psychologists call a high need to achieve, an innate drive that means they thrive on competition and the need to display to themselves (and others) high competence in a competitive arena," he told AFP.
"This is also likely manifested in certain personality traits such as extroversion and conscientiousness.
"There is, of course, also the possibility of some level of narcissism, but that's not necessarily an ingredient as many top athletes are not necessarily self-involved egos."
- 'I need to compete' -
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"However, some feel that need can only be fulfilled in the sport arena and hence they either make high-profile comebacks (with varying degrees of success) or they seek to cross over to other sports."
"I need to compete. I had been trained to compete all my life and I couldn't just walk away from that. I would have bitten my dog."
- 'Small existential crisis' -
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"This makes the athletic retirement process detrimental to the wellbeing of some former athletes... and could cause them to consider a comeback or a pursuit in another sport."