Fads are novel ideas that are rapidly adopted and followed enthusiastically – for a time. By and large, fads are based on bad ideas. Science moves slowly, and caution makes progress more certain. Yet since they can appear new and attractive, fads initially earn great attention. Most end by disappearing from view, sometimes with barely a trace. The American sociologist Joel Best (2006) described these phases as ‘emerging, surging, and purging’.

Not every new idea is a fad. There are real breakthroughs in knowledge, but it can take years to determine how they pan out. As a rule, it is best to remain cautious about concepts that spread rapidly, and to be more welcoming to those that gain support gradually and withstand the test of time. In the end, fads are addictive ideas that short-circuit the slow progress of science. Similarly, fallacies are mistaken conclusions that may be embraced incautiously, but do not bear close inspection. Both fads and fallacies are based on cognitive errors.

Fads, fallacies and cognitive errors

Most people assume that even though others can be foolish, they themselves are rational and show good judgement. This principle has been supported by research (Tversky ' Kahneman, 1982). A lack of critical perspective on the self is the most prevalent of all fallacies. One would like to assume that intelligent clinicians and scientists are less susceptible to fads, and that they only appeal to uneducated non-professionals. If only that were so! This book will show how stubbornly wrong ideas can be held, even by the most brilliant people. It also takes time for fads to decline and disappear, often only after the death of influential founders of schools of thought and their disciples.

One of the earliest books on this subject was Charles Mackay's (1841) Extraordinary Popular Delusions and the Madness of Crowds, still in print after over 170 years. Mackay made fun of faddish ideas, but implicitly assumed that his readers would be immune to them.