Bookending
Bookending means considering a plausible low outcome and a plausible high outcome instead of relying on one forecast. It helps identify what could go wrong, what could go well, and how to prepare for either.
THE IDEA
Bookending (Prepare to Be Wrong)
Bookending is a technique for making decisions under uncertainty, popularized by investor Byron Penstock. Estimate a plausible low outcome and a plausible high outcome. Use both to test the decision and prepare for different futures. In investing, Penstock used the range to compare potential upside with downside; acting near the low estimate is specific to that application.
Example: Coinstar
In 2009, Coinstar's stock dropped 25% after Hollywood studios cut off DVD supply to its Redbox kiosks. Penstock investigated and found Redbox was buying DVDs from Walmart, making the cut-off a nuisance, not a catastrophe. He bookended the stock:
- Lower bookend: $21/share (if Redbox sold all kiosks for replacement value)
- Upper bookend: $62/share (if Redbox thrived)
With the stock at $28 (near the lower bookend), he bought. The stock rose to $46.54 in 10 months. The supplied account reports a 75% return, although that percentage does not match the quoted purchase and sale prices.
Research Support
The source cites work by Jack Soll and Joshua Klayman and by J. Edward Russo and Paul J.H. Schoemaker on overconfidence and judgment. It reports an improvement toward an optimal benchmark (96% vs. 45% without), but this extract does not define the measure. These percentages should not be read as a general success rate for bookending.
Application to Life
- Lower bookend: Create insurance or backup plans (e.g., savings, diversified income).
- Upper bookend: Prepare for unexpected success (e.g., scalable operations, capacity).
Considering a range can expose assumptions hidden by a single best guess. The chosen bookends remain estimates, so outcomes can still fall outside them.
When to use it
Evaluating a stock investment by considering both a crash scenario and a boom scenario.
Deciding on a career change: bookend the best and worst financial outcomes over the next five years.
Budgeting a project: estimate a minimum viable outcome and a stretch goal, then plan resources accordingly.
Preparing for a new hire: consider the best-case contribution and worst-case liability, and create contingency plans.
FROM THEORY TO EVERYDAY LIFE
In practice
Byron Penstock and Coinstar
In late 2009, investor Byron Penstock evaluated Coinstar stock after studios cut off Redbox. He estimated a lower bookend of $21 (liquidation value) and an upper bookend of $62 (success). The stock fell to $28, near the lower bookend, so he bought. It rose to $46.54 in 10 months, with a reported 75% return. That percentage is inconsistent with the quoted prices, so the account needs checking before being used as a return calculation.
Research on Overconfidence
In a study by Soll and Klayman, participants estimated movie box-office receipts. When asked to consider only a best guess, their 80% confidence intervals contained the true value only 39% of the time. When they explicitly considered low and high bookends, the account reports performance at 96% of an optimal benchmark. The extract does not define that benchmark, so it cannot be directly compared with interval coverage.
A MOMENT TO REFLECT
Put it to work.
What are the best and worst possible outcomes of a decision you are currently facing?
How can you insure yourself against the lower bookend (worst case)?
If success far exceeds your expectations, how will you scale or capitalize on it?
Often confused with
References
- Overconfidence in Judgmental Forecasting — Jack Soll and Joshua Klayman (2005)
- Decision Traps — J. Edward Russo and Paul J.H. Schoemaker (1989)
CONTINUE THE CONVERSATION
Source texts
- Decisive How to Make Better Choices in Life and Work (Chip Heath)