The New York Times reports that there is no  scientific proof that a diet high in fats affects mortality. In the course of that article, the author notes:

Dr. Koop was expressing the consensus. He, like the architects of the federal "food pyramid" telling Americans what to eat, went wrong by listening to everyone else. He was caught in what social scientists call a cascade.

We like to think that people improve their judgment by putting their minds together, and sometimes they do. The studio audience at "Who Wants to Be a Millionaire" usually votes for the right answer. But suppose, instead of the audience members voting silently in unison, they voted out loud one after another. And suppose the first person gets it wrong.

If the second person isn't sure of the answer, he's liable to go along with the first person's guess. By then, even if the third person suspects another answer is right, she's more liable to go along just because she assumes the first two together know more than she does. Thus begins an "informational cascade" as one person after another assumes that the rest can't all be wrong.