Optimism Bias Adjustment
Correct forecasts with the error pattern from comparable past outcomes
- Difficulty
- Moderate
- Time to result
- ~weeks to results
- Steps
- 5
- Confidence
- 98%
Optimism improves motivation but can make people underestimate cost, duration, and risk. This framework separates the useful belief from the operational forecast. First capture the estimate, its evidence, and confidence before the outcome is known. Then use similar completed cases—or a personal prediction ledger—to compare forecasts with actual results. Calculate the recurring error and add that correction to the new estimate. Afterward, diagnose whether missing information, overconfidence, or another factor produced the miss, and turn that finding into a policy for future decisions. The mechanism preserves forward momentum while using outside-view evidence to protect plans from predictable bias.
Origin
Sharot used the British government's Green Book and London Olympics planning to show how past project overruns can correct optimistic estimates.
Core principles
- 01Optimism can motivate action while still distorting forecasts
- 02Recorded outcomes are more reliable than remembered impressions
- 03Comparable past projects expose systematic estimation error
- 04A policy can correct behaviour without forcing pessimistic beliefs
How to run it
- 1
Capture the forecast
Write the expected duration, cost, return, or performance before events unfold. Record the evidence available and your confidence level.
Pro tip Use a fixed template so repeated decisions become comparable.
Watch out Do not reconstruct the forecast after learning the outcome.
- 2
Choose comparable cases
Find similar completed projects or earlier decisions of your own. Keep the comparison class close enough that its errors are informative.
Pro tip Prefer actual forecasts paired with actual outcomes, not general recollections.
Watch out Cherry-picking one unusually successful case preserves the bias.
- 3
Measure the error
Compare predicted and actual results across the cases and calculate the typical gap. Note whether the bias affects time, cost, returns, or several dimensions.
Pro tip Use an average across multiple cases when possible.
- 4
Adjust the estimate
Add the historical bias to the current forecast or budget. Keep your motivating goal, but operate from the corrected number.
Pro tip Make the adjustment a default policy rather than a matter of mood.
Watch out A correction factor is not a guarantee; uncertainty still remains.
- 5
Diagnose and update
When the outcome arrives, record it and identify why the estimate missed. Update the correction policy with the new evidence.
Pro tip Separate missing information from overconfidence so the remedy targets the cause.
In the wild
Government appraisers examined earlier Olympics, comparing predicted cost and duration with actual results. They calculated the average bias and added it to estimates for the London Olympics rather than asking planners to become pessimists.
→ The plan incorporated a systematic correction for predictable optimism bias.
An investor records each expected profit, the information available, and confidence at the time. After enough outcomes, the investor sees a recurring overestimate and discounts future projections by that observed gap.
→ Future decisions use calibrated expectations instead of memory or confidence alone.
Common mistakes
Trying to eliminate optimism
The aim is to correct decisions, not destroy the positive expectations that support motivation.
Keeping forecasts in your head
Memory changes over time, so an unwritten estimate cannot provide a trustworthy error record.
Ignoring the reason for the miss
A numerical adjustment helps, but diagnosing missing information or overconfidence produces a better policy.
Is it for you?
Best for
It is best for repeated or comparable decisions such as projects, investments, hiring, renovations, and budgets.
Not ideal for
It is not ideal when no meaningful comparison set or outcome record exists.
From the transcript
“looked at the predictions of how long it would take, how much it would cost, and then the actual how long did it take, how…”
“write down what you think is going to happen. Okay, now go back and adjust it according to what we know from past experience is…”
“while making your estimate, it's good to also record, what do I know at the moment, right? Which upon which I'm making this prediction. Um…”
From the episode
Tali Sharot: The Neuroscience of Positivity, How Our Brains Create Our Future
Tali Sharot