I am 80 feet up a sheer cliff, with one foot on a ledge about as wide as a finger, the other dangling, while I try to get my sweating hands to cling to the bulging rock in front of my face. I am breathing hard, and very scared. Some feet above I can see a break in the rock, the next hold I am aiming for. If I don't reach it, I'll surely fall off - probably 10 or 15 feet, until the ropes attached to my waist stop me, and bang me into the cliff. It'll certainly hurt. I can almost hear the adrenalin washing through my head. It's wonderful, a great way to spend a Sunday afternoon.

Stephen Thornley doubtless knew the feeling, too. He was the British leader of a mountaineering expedition in Pakistan, an experienced climber who with two colleagues was declared dead this week after being hit by an avalanche.

Afterwards, Stephen's father said: "I was hoping he would do this and then give it up." The truth, however, is that for many people such sports are the only way to make life worth living. If Stephen had conquered that peak, he would have had his sights set on others, too. The common phrase is "adrenalin junkie": someone addicted to the high of real danger.

Cave-diving, potholing, rock climbing, motorbike and stock-car racing, cliff-diving, hang-gliding - all carry inherent risks, which to their devotees make them delicious in an increasingly safe world, where drugs have conquered old diseases, and better engineering has made cars and airplanes far safer than in the post-war years.

There are fatalities in all these sports, yet the really dangerous activities are those that we do not usually class as risky. Diving and swimming, along with horse-riding and rugby, cause far more broken necks than any "risk" sport. A higher proportion of people who swim beyond their depth off the British coast die than in mountaineering.

So why don't we talk of equestrianism, rugby and swimming in the same breath as cave-diving? Nobody looks at a rugby game and declares that it looks like a prime place for a serious injury, yet anyone gazing into the dank mouth of a pothole knows on a visceral level that it can't be a good place to get caught when the rain starts. Equally, people think that bungee-jumping is a harmless thrill, rather than a real risk - unaware of the fact that the shock at the bottom of the fall can damage the retina. To a real adrenalin junkie, it's the latter fact that would make the jump worthwhile.

At a time when we're surrounded by safety, hemmed in by cotton wool and told not to open interesting latches and intriguing doors, it's perverse and pointless to do dangerous things - which is exactly why some people have to do it. Stephen Thornley wasn't the first, and he won't be the last.