when there was a visibly clear road in front of the ill-fated lane
switchers.
The patrolman’s account provides certain insights into the way we
respond to social proof. First, we seem to assume that if a lot of people
are doing the same thing, they must know something we don’t. Espe-
cially when we are uncertain, we are willing to place an enormous
amount of trust in the collective knowledge of the crowd. Second, quite
frequently the crowd is mistaken because they are not acting on the
basis of any superior information but are reacting, themselves, to the
principle of social proof.
So if a pair of freeway drivers decided by coincidence to change lanes
at the identical moment, the next two drivers might well do the same,
assuming that the forward drivers had spotted an obstruction. The
resulting social evidence confronting drivers behind this group would
be potent—four successive cars, all with their turn signals flashing,
trying to angle into the next lane. More signal lights would go on. The
social proof would be undeniable by then. For drivers to the rear, there
could be no question about the correctness of switching lanes: “All those
guys ahead must know something.” So intent would they be upon
working themselves into the next lane that, without even checking the
true condition of the road before them, the drivers would begin a line-
long flank assault. Crash.
There is a lesson here: An automatic-pilot device, like social proof,
should never be trusted fully; even when no saboteur has fed bad in-
formation into the mechanism, it can sometimes go haywire by itself.
We need to check the machine from time to time to be sure that it hasn’t
worked itself out of sync with the other sources of evidence in the
situation—the objective facts, our prior experiences, our own judgments.
Fortunately, this precaution requires neither much effort nor much
time. A quick glance around is all that is needed. And this little precau-
tion is well worth it. The consequences of single-minded reliance on
social evidence can be frightening.
This aspect of the social proof phenomenon always reminds me of
the way certain Indian tribes—the Blackfeet, Cree, Snake, and
Crow—used to hunt the North American buffalo. There are two features
of buffalo that make them especially susceptible to erroneous social
evidence. First, their eyes are set in their heads so that it is easier for
them to see to the side than to the front. Second, when they run, as in
a stampede, it is with their heads down low so they cannot see above
the herd. As a result, the Indians realized, it was possible to kill tremend-
ous numbers of buffalo by starting a herd running toward a cliff. The
animals, responding to the thundering social proof around them—and
never looking up to see what lay ahead—did the rest. One astonished
Robert B. Cialdini Ph.D / 123