Once upon a time there were some schoolboys. They were lazy and wanted to escape from their studies. One of them suggested that they should make their teacher feel ill by telling him how terrible he looked. Thus it was that, as soon as the master arrived at the school, one boy after another told him that he was looking ill. At first the teacher told the boys that he was quite well, and that they were imagining things; but, as more and more boys, apparently spontaneously, described him as looking ill, he began to feel it himself. Returning to his house, he told his wife that something was wrong with him. She said that she thought that it was his imagination, but he insisted that he was near to death, and took to his bed, even accusing her of being insensitive to his sufferings

From Idries Shah’s The Hundred Tales of Wisdom, London: The Octagon Press, 1978, p. 155.