Anchors and Herd Behavior
Two of the book's core behavioral mechanisms: psychological anchoring to recent prices, and the social pressure to follow the crowd.
Shiller draws directly on behavioral economics and psychology to explain how exuberance sustains itself once started. Anchoring is the tendency for people's estimate of a fair or reasonable price to be unduly influenced by a reference point — often simply the current or recent price itself, rather than any independent calculation of underlying value — meaning that as prices rise, investors' own internal sense of what counts as "expensive" quietly rises along with them, making genuinely extreme valuations feel normal to anyone anchored on recent trading history rather than a fundamentals-based calculation.
Herd behavior compounds this: individuals face genuine social and professional pressure to follow prevailing opinion, since being wrong in the same way as everyone else carries less career and social risk than being wrong alone — a fund manager who missed a bubble's gains while colleagues profited faces real professional consequences, creating an incentive to participate even when privately skeptical. Shiller treats this as a rational individual response to an irrational collective outcome — participating in a bubble one privately doubts can be the individually sensible choice given the actual incentives faced, even while the aggregate result is collectively irrational.
| Mechanism | Effect |
|---|---|
| Anchoring | Fair-value judgment drifts toward recent prices rather than independent fundamentals |
| Herd behavior | Individually rational to follow the crowd, even when privately skeptical, due to career/social risk of being wrong alone |
A common objection to bubble theories is that plenty of highly intelligent, well-informed people participated in the dot-com bubble — surely they knew better? Shiller's herd-behavior analysis directly resolves this apparent paradox: participating is not necessarily a failure of intelligence or analysis, but can be the rational response to a real incentive structure where deviating from the crowd carries asymmetric personal risk (looking foolish or losing clients/job for sitting out a boom that continues) relative to the risk of participating alongside everyone else in a bust that, when it comes, damages nearly everyone simultaneously and is therefore less personally/professionally costly to have been wrong about.
- Anchoring means fair-value judgments drift toward recent prices rather than an independent fundamentals-based calculation as prices rise.
- Herd behavior can make participating in a bubble the individually rational choice given real career/social incentives, even for someone privately skeptical.
- This resolves the apparent paradox of intelligent people participating in bubbles — it isn't necessarily a failure of analysis, but a response to real incentives.