But Edinburgh businessman Karteek Clarke just can't leave a challenge alone. He gave it another go – becoming the first Scot to attempt the crossing twice. Then he did it again, and again, and again.
Incredibly, the 42-year-old business training consultant from Newington has now completed his tenth swim to France – and he puts his remarkable achievement down to meditation and yoga.
He said: "Every time I do it I say it will be my last time, but this time so many events conspired to draw me back to Dover to give it another try.
"I first attempted it back in 1994 and I thought I could complete it with very little training, but I had to give up after I'd been going for 12 hours and still hadn't even made it halfway.
"I went back and trained properly and completed the crossing in 1997, and a friend of mine filmed me coming out of the water saying that it was great but that I was never doing that again. It was just too tough."
Mr Clarke spent a few years pursuing less gruelling athletic challenges, such as swimming Lake Zurich in Switzerland.
"It's only 17 miles across and it's a bit warmer," he said. "It's hardly a dip in the pool but it's nothing compared to the Channel."
However, the Channel drew him back once more in 2000, and has refused to let him go since.
He says he has been continually drawn to cross-Channel swimming by his devotion to the Sri Chinmoy discipline of yoga and athletic endurance.
On his latest trip, completed on 13 August, he was monitored from a boat by "King of the English Channel" Kevin Murphy, the male world record holder with 34 crossings under his belt.
Mr Murphy's feat is dwarfed only by the "Queen", Alison Streeter, who has crossed the Channel an impressive 43 times.
Mr Clarke said: "I'm definitely not racing to catch up with these guys.
"I keep going back to hone my meditation skills as our Sri Chinmoy teacher encourages us to undertake these tasks to promote self-discipline. Like most brands of yoga, the aim is to silence the restless mind and purge it of negative thoughts. After about six hours in the water, you're cold, wet and miserable, but it starts to become quite exhilarating."
This time, the choppy seas, showers and swell made conditions difficult, and Mr Clarke had to battle seasickness which led to his energy levels dropping.
He finally paddled up the shore at Calais 16 hours and 59 minutes after setting off. The world record for a cross-Channel swim is just under seven hours.
Mr Clarke is one of a select few swimmers who have repeatedly crossed the Channel.
Michael Oram, honorary secretary of the English Channel Swimming and Piloting Federation, said: "Very few people have swam the Channel more than ten times, and while Mr Clarke has his spiritual motivations, others are motivated by the challenge.
"The Channel is the Everest of swimming, and I would argue that it's even tougher than climbing Everest because there have been so many ropes and handrails added over the years that you can just stroll up it now. More than 4,000 people have climbed Everest but only around 1,000 have swam the Channel because it's all about the endurance."