Need for speed and thrills drives all the greats
Formula One drivers are a special breed, intensely competitive thrill seekers driven by a need for speed and thirst for adrenalin.
Michael Schumacher, in critical condition in hospital with head injuries suffered in a skiing accident in the French Alps, would not have been the seven times world champion he was without those qualities.
The world of Formula One was praying on Monday for that determination and fighting spirit to see the retired 44-year-old through a greater battle than anything he experienced on the racetrack.
Leaving the grand prix paddock can be a challenge for racing drivers, many of them still relatively young and accustomed to living life on the limit, who must seek their thrills elsewhere.
Schumacher took up motorcycle racing soon after he first retired from Ferrari in 2006, injuring his neck in a 2009 crash. Others, such as Australian Mark Webber who broke his leg while riding a mountain bike in an endurance event in Tasmania in 2010, have moved on to Le Mans.
"Michael loves to challenge race tracks on superbikes and he often excitedly shows his many amazing skydiving pictures on his phone," said the German's former Benetton team mate Martin Brundle, now a commentator for Sky television.
"He's only a year out of the F1 cockpit but, as a driven and competitive person, you can't simply switch off and settle down at the end of a long career, you need challenges and achievements to keep the adrenalin flowing.
"It's not uncommon for racers to survive many big accidents to then be injured in cars, aviation, bikes, on water, or indeed ski slopes. The need for machinery and speed will always be there, it's inevitable," added the Briton.
Just as many professional Alpine ski racers have a fascination for fast cars and motorbikes, so do fitness-obsessed racing drivers exhibit a love of extreme sports.
"Part of the reason that ex-drivers enjoy sports like skiing is because the physical rush that you get from the skis, through your feet and whole body and the adrenalin surge, is something you become an addict to," former grand prix winner John Watson told BBC radio.
"Michael Schumacher raised the level of driver fitness and training...and part of his enjoyment of being a grand prix driver was extending the limits that were known at the time of race drivers' fitness, both physical and mental.
"It becomes habitual...if you are somebody like Michael Schumacher, that's a part of what your life is even though you are not directly involved in a competitive sport."
Ferrari always used to have an annual January gathering with their drivers in the Dolomites and Schumacher impressed with his skiing ability.
The German was on vacation with his family, skiing off-piste in the resort of Meribel when he fell and banged his head against a rock.
He was wearing a helmet and, by all accounts, skiing well within his capabilities. The accident was widely seen as a freak.
In the old days when safety was virtually non-existent, those who made it through to retirement were the lucky ones. Even then, fate could be especially cruel.
Britain's Mike Hawthorn walked away from the sport in October 1958 as his country's first world champion. He died months later when he crashed his Jaguar sportscar into a tree.
Compatriot Mike Hailwood, a champion on two wheels and podium contender in F1 in the 1960s and early 1970s, died in a 1981 car collision after popping out to buy a fish and chip supper.
French ex-Ferrari driver Didier Pironi was killed in 1987 while racing a powerboat.
Even some of those still racing find they need an extra adrenalin fix. As the sport has become safer, with Formula One's last driver fatality the death of Brazilian Ayrton Senna in 1994, the dangers elsewhere have become more apparent.
Poland's Robert Kubica almost died, and certainly ended a Formula One career that could have led him to Ferrari, when he crashed in a minor rally in Italy in 2011.
Ferrari's 2007 champion Kimi Raikkonen, who has also raced powerboats and rally cars, hurt his wrist in 2011 in a snowmobile incident.