The mother of my children is scared of heights; half a lifetime spent in Edinburgh, yet the Scott Monument remains unvisited by her.

Likewise the enormous Ferris wheel that appears every Festival and Hogmanay season. And don't even mention Salisbury Crags.

Even a less obviously vertiginous attraction such as the annual Doors Open Day event can be a challenge. It was this year, anyway. When the kids and I decide to climb Corstorphine Hill Tower in the west of the capital, we have to leave the fourth member of our party behind to indulge her acrophobia at ground level. We take the chocolate, though.

Perhaps "indulge" isn't the most generous word to use. But, to my mind, hers is an irrational fear and, in the face of the irrational, I often find sympathy in short supply. After all, it's clear the tower isn't going to fall down. It's clear the five-feet-high parapet enclosing its viewing platform is more than capable of preventing accidents. There will be no earthquake, no drone strike, no act of God. So what's the problem?

I come back to all this (danger, phobia, sympathy, rationality and its opposite) while watching fourth-generation tightrope walker Nik Wallenda inch along a high wire strung between two Chicago skyscrapers on Monday.

As millions watch on television and thousands more gawp from the streets below, the 35-year-old American walks the length of two city blocks, only 600ft up in the air and with no harness or safety net. He then makes a shorter walk, still with no harness or safety net, and this time wearing a blindfold into the bargain; a bargain that looks for all the world like the sort you make with the Devil.

It makes me wonder who is more irrational. Is it the risk-taking show-off with the head for heights, whose bird's eye view of the Windy City may be the last thing he ever sees? Or the person who sits out a short climb up a solid stone building that has stood for 100 years and will stand for 100 more?

Well, in a sense it doesn't matter. They're both extreme versions of the same thing. What does matter is that viewing someone at one end is helping me better comprehend the people at the other: five per cent of the population with the most severely afflicted experiencing problems on an almost daily basis. And I feel the stirrings of sympathy at last. So next time I climb a tower alone with the kids, I won't tut-tut or try to deploy logic against apparent unreason. Instead I will be understanding. Hey, I might even hand over the chocolate.