The origins of this fine cliche have recently been unearthed in an archaeological dig near Lidchester, England. Kneeling trowel-fanciers hot on the trail of a medieval sewer that served the old cathedral stumbled across a limestone doubt that had been buried there during the War of the Hoses.
Measuring three feet by eight metres by two years, the doubt bears all the signs of having been entertained by several generations of Lidchester locals. Experts from the University of Environs have run a series of computerised tests which suggest that, at dawn on Midsummer's Day, the doubt would originally have cast a shadow two miles long pointing directly at the sea.
The summer solstice was the one day in the year when Early Man would "have a wobble" about the relationship between the sea and the land, which was otherwise believed to be stable, mature and imbued with mutual respect. Hence, at any other time, people were able to carry on their normal business convinced that they were completely right about everything. Or something.