Dear Economist,

I have a long-running argument with my husband. He always reverses into parking spaces. I prefer to drive in forwards and reverse out. Who is correct?

Yours sincerely,

Maddie French, Cirencester

Dear Maddie,

Your question takes us into deep waters. Start by observing that it is, presumably, easier to drive forward than to reverse. Your husband is therefore delaying gratification while you are delaying difficulties. Mainstream economic theory is perfectly clear on this point: your husband is being silly. It is pain, not pleasure, which should be delayed, if for no other reason than we are all mortal.

But our analysis must go further than this. If you park for an hour, even a slight difference in ease of reversing in versus reversing out should swamp any benefits from delaying the difficulty. For example, if it is just one-tenth of one per cent harder to reverse out than to reverse in, then you should reverse in. If you preferred to delay the pain by an hour, bear in mind that one-tenth of one per cent per hour compounds to a substantial annual interest rate: around one-third of a million per cent. To drive in forwards and reverse out would show either impatience verging on insanity or a staggering incapacity to predict the near future.

There is another consideration: you are trading off reversing under conditions of certainty versus reversing under conditions of uncertainty. You do not know what the car park may look like in an hour, whether it will be crowded, or whether you will be in a hurry. Having to reverse out under adverse circumstances is a low- risk but high-impact event. My advice is position yourself ready to leave at a moment's notice: the car park at Safeway can be an unpredictable place.

This week's Economist is Tim Harford, an FT Peter Martin fellow. www.timharford.com

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