Some villagers were going to celebrate an important wine festival in a few days' time, so they borrowed a huge barrel from the nearest town, put it in the village square and determined that each of them should empty a bottle of the best wine he had into it, so that there should be plenty at the feast.
One of the villagers thought he would be very clever. 'If I pour a bottle of water in, instead of wine, no one will notice it,' he said to himself, 'because there will be so much excellent wine in the barrel that the water will be lost in it.'
The night of the feast arrived. Everybody gathered in the village square with jugs and their glasses for the wine. The tap on the barrel was opened - but what came out was pure water. Everyone in the village had had the same idea.