They have multiple reasons for being and tie into broader demographic and economic trends. The health and fitness trend, for instance, connects with fear of death, aging, the desire to look good and to have a positive self-image. The countertrend to drink, smoke, and eat fatty foods also runs deep. It ties into what I call the need to be naughty. And, of course, young people remain convinced of their invulnerability.
Fads are most likely to become trends when they are anchored to deep needs.
As we try to predict the future, we need to guard unrelentingly against seeing a trend in every fad or rationalizing a trend because the logic, to all appearances, is so persuasive. Qualitative research helps us by providing insight into the motivations that underlie the fads, trends and, equally important, the counter trends. But it is the mainstreamers who, with their watchful waiting, signal that a full-blown trend has arrived and is likely to be around for a good long while.