He cites a recent example in the field of health science -- an international hysteria over dietary fat. There are many other instances he could have used.
Social scientists call it "cascade theory": the idea is that information cascades down the side of an "informational pyramid", like a waterfall. It is easier for people, if they do not have either the ability or the interest to find out for themselves, to adopt the views of others. This is, without doubt, a useful social instinct. As it has been put, cascade theory reconciles "herd behaviour" with rational choice, because it is often rational for individuals to rely on information passed on to them by others.
Unfortunately, it is less rational to follow wrong information, and that is what can often happen. We find people cascading uselessly - like so many wildebeest fleeing a non-existent lion - in so many everyday ways. A lot of economic activity and business behaviour, including management fads, the adoption of new technologies and innovations, not to mention the vexed issues of health and safety regulation, reflect exactly this tendency of the herd to follow poor information.
We live in an age of hype, against which we have few defenses other than an all-encompassing skepticism and that may well even more destructive than the mad oversold schemes with which we are now regularly afflicted.