In 2004 I did a programme called The Rebel Billionaire for Fox Television, where I was nice to people and then had to whittle them down to a winner. In one episode, I told a participant we were going to be the first to go over the Victoria Falls in a barrel. Annie Taylor was the first person to conquer the Niagara Falls in Canada, riding the 170-foot drop in an airtight wooden barrel in October 1901. Since then many other daredevils have copied her achievement. But the Victoria Falls in Africa – at 360 feet – is more than twice as high, and much more dangerous, with jagged rocks at the bottom. I asked one of the contestants, Sam Heshmati, if he was ready for the challenge of going over the falls with me, in a barrel I said had been specially created by NASA.

Were we going to do this thing? Bravely, Sam nodded. We got into the barrel. A large crane lowered us into the fast-flowing river, a few metres away from the drop. A two-minute countdown began. It seemed an eternity, Five. Four. Three. Two . . .

A split second before we were due to plummet, I shouted: 'Stop! Hold on just one moment, I want to show you something.'

So we got out. And I showed young Sam the bottom of the falls. I pointed at the rocks below.

'Sam,' I admonished him, 'you were ten seconds from certain death. You shouldn't blindly accept a leader's advice. You've got to question leaders on occasions.'