So it's a mistake, and will be sorted out within minutes. You are invited to step out of the vehicle and as you do, you realise, to your stupefaction, that this is not, after all, your car. Similar, yes, but not your car. The world has turned upside down.
As it did this week to Wiltshire man Bill Ives. He drove off in Alan Burch's red Fiesta, which Mr Burch had parked next to Mr Ives' car - also a red Fiesta. Mr Ives just unlocked the door of the first one he came to and assumed it was his, failing to notice that he had lost a sun-roof and gained 21,000 miles on the clock.
This incident reminds me of a story of the old Soviet Union. A Moscow man is in Leningrad for a meeting. Getting blind drunk that night, he takes a number 10 trolley to a suburb of tower blocks instead of returning to his hotel. There, he ascends in an identical smelly lift, alights at the same floor in front of a familiar front door, turns his key in the lock, and snuggles up to a warm, voluptuous female form in bed. Only when dawn breaks does he realise that he is actually 500 miles from home. By this time, consummation has occurred, love has blossomed and it is all too late.
You might expect such things to happen a great deal, with all this cultural homogeneity and the hold that fashion has on us all. Parents of adolescent boys must be particularly hard-pressed to distinguish their shambling, reverse baseball-capped Beavis from someone else's Butthead. Furthermore, many of us develop highly sophisticated and extremely repetitive ways of doing things - standing in a particular place for the train every morning, always starting with the fruit when shopping at Safeways. That way, our brains are free for important fantasies and plots. We go automatic.
Last week, for instance, a Newport man came home in the wee hours to discover the back door broken down and an interloper upstairs, asleep in bed. Tommy McQuade managed to subdue the strangely confused burglar until the police arrived. It turned out that the chap had lived in the house until 18 months before, and, after having attended a lively stag evening, some forgotten internal navigator - like the kind of homing device that brings turtles thousands of miles across trackless ocean to lay their leathery eggs - guided the man back to Mr McQuade's.
So far, so good. But what is remarkable about this incident is how the intruder then ignored all the warning signs that maybe he had made a mistake. The first must have been when his keys did not fit the lock. The second, presumably, when his girlfriend failed to answer his calls for help. But even when he was engaged in breaking down the door, the light of realisation did not shine in the drunk man's head.
Actually, such obtuseness (or absent-mindedness) is very rare. Most of us are, in reality, highly attuned to virtually any variation from the expected. We surround ourselves with thousands of mental and physical trip-wires, which - if set off - alert us to abnormality. Our environments may look very similar, but in a million ways, we have coded them just for us and just for now.
Otherwise, God knows what would happen. How many of us still have keys that fit the locks that guard old flames and cast-off lovers? Perhaps, like Miss Havisham, they have remained unchanged, mouldering, waiting for this day. "Darling!", they mumble toothlessly, as you barge in, "I knew you would come back one day! Cake?"