Hurrah for exploding props and nosy dogs

Sadler's Wells isn't where you go to hear folk tunes; it's the home of top-flight ballet. But the audience at Thursday's opening night of Petrushka was treated to a brief burst of Irish song when – after a cock-up with a rope ladder – the director burst on stage to keep everyone entertained. It was a brilliant bit of improvisation by Michael Keegan-Dolan, the youthful Dubliner. He sang; the hitch was fixed, and a warm fuzzy feeling enveloped the auditorium when the show went on. Everyone felt they were in it together.

So often, disaster comes hand in hand with delight. A friend's wedding vows were interrupted by the entrance of the vicar's dog. It wondered in, sniffed the bride and bridegroom, and ambled off – but not before establishing a place in future family lore. Once the worst has happened, what's left to worry about?

In politics, the master of disaster is Boris Johnson. He knows that dangling suspended on a zipwire like a giant baby is worth thousands more votes than an earnestly delivered pledge. Perhaps the reason scandals never stick is that he doesn't try to present an image of perfection. Quite the opposite. He ruffles his hair instead of smoothing it. I am a human, not a PR suit, is the message. Being first to admit an imperfection is the most effective way to deflate your critics.

Wimbledon, our beloved summer tennis tournament, fetishises formality and close-cropped perfection. The stripes, the whites, the coil-sprung ballboys and that ceremony with Princess Anne. But apart from the tennis, what do we love most? Not the strawberries, not Sue Barker, but the hope of Cliff Richard, who pops up when it all goes to pot. It rains, he sings, and a weird sentimental love of humanity descends over SW19. It's not at all British, and yet, it absolutely is.

As Jenny Gilbert writes in her review on page 56, Thursday's ballet at Sadler's Wells was a four-star show improved, not worsened, by disaster. Jeremy Beadle spotted the joy of the boo-boo years ago, with You've Been Framed!, spawning a whole new genre of bloopers as entertainment. But the pleasure here is not of Schadenfreude, of revelling in another's discomfort, but of sharing in the embarrassment. It follows in the tradition of pantomime, a momentary inversion of the norm. That programme went off badly only when they started to show accidents that looked genuinely painful.

At the theatre, cock-ups can leave a sour taste if you've been left with little change from £200 for a night out for two, but some blunders are priceless. I would have paid good money to be in the house the night a phone rang uncued on stage, only to be answered with presence of mind by an actor nearby. Handing it to another character, he intoned: "It's for you."

After all, how often do we look back on a play or musical and recall a brilliantly delivered line? Chances are, it's the collapsing chair that stays with you for ever.