If you see people pulling something behind them these days, especially during the holiday season, it is more likely to be a bag than a dog. The invention of the wheelie is one of those things - such as hard hats and shopping trolleys - that seem so blindingly obvious in retrospect it is a wonder it did not happen earlier. But it did not.

All of them needed someone with a bright idea and the courage to follow it through. Why on earth did people lug heavy suitcases everywhere when such a simple solution was at hand? It was not until the late 1980s when Robert Plath, a Northwest Airlines pilot, fed up with carrying his gear around airports, added wheels and a proper handle to his suitcase that change happened. Since then dozens of incremental improvements have been made including telescopic handles and better wheels.

Not everyone approves, particularly those at the receiving end of a battalion of them thundering down the platform or collecting at the bottom of an escalator. One London blogger called them "the instruments of the devil" used by people who decelerate without warning and fail to signal before swerving in front of you. Clearly he thinks there ought to be some kind of driving test. But to most travellers they are one of those unsung inventions that make life a bit easier and reduce back strain. The past few days could have been even worse for the thousands stranded in airports as a result of the terrorism threat but for a pilot's bright idea less than 20 years ago.