Once in a while, it pays to miss a flight. In his new book, How Not To Be Wrong: The Hidden Maths of Everyday Life, Jordan Ellenberg explains that if you have enough time to do leisurely shopping and reading at an airport, you've turned up too early for your flight.
As he explains in Chapter 12 (Miss More Planes), if you never miss a flight, you are allowing too much time. In his book, "allowing" equals "squandering".
Good mathematics, like the best kind of travel, is about simplicity. It is oversimplifying his argument only a little to say that, if you are missing one or two flights in every 100 because you reach the airport too late, you have something close to the optimum strategy for timing your run to the airport.
You might, by adding an hour to your arrival time, be able to eliminate those one or two missed departures but, in the process, you would waste the equivalent of four days in the purgatory of the modern airport.
The late Nobel-prizewinning economist George Stigler long held that "if you never miss the plane, you're spending too much time in airports". But he was a member of the Chicago School of Economics, which at the time was served by the world's busiest airport. If you missed the 7am to New York or LA, there would be another in a few minutes.
Even among airlines that sell forgiveness, the price of missing the deadline is high. The formula for you and me does not require analysis of "utils" and identifying a point on the Laffer curve, as Ellenberg outlines. It involves eliminating all the uncertainties you can, then building in a bit of padding.
1. No checked-in luggage. You don't need it. By taking only carry-on you eliminate the risk that your bag will go off on its own little holiday.
2. Check in online, print out your boarding pass (or save it to your smartphone).
3. Choose public transport that runs to a published schedule. Work out the last possible departure you can take that will allow you to reach the airport one hour before your plane is due to go. Then take the previous departure.
That means the only airport uncertainty you face is the length of the security queue. But what an unpredictability: typically, the airport's "service-level agreement" requires the procedure to take less than, say, five or 10 minutes, 95 per cent of the time. That means on one occasion in 20, it will be longer. And you and I don't know when.
When you get unlucky, take advantage of the fact that almost all your fellow passengers will have allowed too much time, and ask politely if you may jump the queue.
Like all good rules, this formula has exceptions...
I turned up six hours before my flight from Melbourne because I was determined to be first in the queue at check-in and get an extra-legroom seat.
Amsterdam Schiphol and Singapore Changi are so full of airside distractions (such as, respectively, a Rijksmuseum outpost and a rooftop swimming pool) that they deserve some "dwell time".
If you are heading for a wedding, funeral or job interview, the downside of missing the flight is so huge that you should wisely add a large dollop of extra time.
When the journey to the airport and through security goes smoothly, you might want to buy How Not to be Wrong. But don't get so engrossed that you miss the last call.