Hindsight bias - I should have known!

Part 2 - A Decision is a Bet on the Future based on our Beliefs

Highlights

Hindsight bias …

• causes us to give an outsized probability weight to an outcome result (“I should have known!”).

• is the tendency to believe an event, after it occurs, was predictable or inevitable.

• distorts our memory of what we knew at the time the decision was made (aka, “memory creep”)

• combined with resulting (outcome bias),

  • reduces our ability to learn from experiences and improve our decision-making

  • causes us to blame others or ourselves for bad outcomes

  • causes us to have less compassion for others or ourselves when there is a bad outcome

  • causes us to take outsized credit for good outcomes

In Part 1 — A Decision is a Bet on the Future based on our Beliefs — I reviewed outcome bias or resulting. In brief, resulting is a systematic bias; it is a biased retrospective analysis where we use a good or bad outcome to draw conclusions about the quality of the decision process. Resulting prevents us from evaluating the quality of our decisions, and it prevents us from learning from our experiences. Resulting causes us to learn the wrong lessons. Even worse, bad outcomes are often filled with negative emotions which may prevent us from thinking straight.

A second cognitive bias that affects our ability to learn from our experiences is hindsight bias. “Hindsight bias is the tendency to believe an event, after it occurs, was predictable or inevitable.”¹ If a rare event occurs to us, we give greater weight to the probability of its occurrence.

“Hindsight bias is the tendency to believe an event, after it occurs, was predictable or inevitable.”²

“The hindsight bias describes our tendency to look back at an unpredictable event and think it was easily predictable. Also called the “knew-it-all-along” effect, this bias occurs when our current knowledge of an event’s outcome influences our perception of past decisions or judgements, causing us to overestimate our ability to predict future events.”

Figure 1: Sources of uncertainty in decision-making: Imperfect information and luck

Figure 1 depicts the sources of uncertainty in making decisions — imperfect information and luck (random chance, variability). The imperfect information includes what we know about the probabilities of the possible outcomes at the time a decision was made.

Example 1 - Vaccine hesitancy

For example, suppose I choose to vaccinate my infant with the MMR vaccine as recommended by my pediatrician to prevent measles, mumps, and rubella. Unfortunately, my infant suffers a febrile seizure.³ In spite of reassurances from my pediatrician, I decide to not complete the MMR series with my infant. Hindsight bias can distort what I learn from my first decision (vaccinated my infant) and influence subsequent decisions (decision not to complete vaccine series). Figure 2 is a model of hindsight bias.⁴ With hindsight bias, our memory of what we knew at the time of the decision is distorted (aka, “memory creep”), we feel the outcome was inevitable, and/or we express that we saw the outcome coming.

Figure 2: A model of hindsight bias. This model emphasizes unique interconnections between inputs and consequences with regard to three levels of hindsight bias: memory distortion (“I said it would happen.”), inevitability (“It had to happen”), and foreseeability (“I knew it would happen”). (Adapted from Neal, 2012, and The Decision Lab.)

Hindsight bias affects all of us, and it can contribute to vaccine hesitancy, even in the middle of a measles outbreak. The Washington Post reported the experiences of Ms. Kaleigh Brantner in Texas who continued to choose not to vaccinate her child even in the midst of a large and growing measles outbreak.⁵

“Brantner, 34, said she decided not to vaccinate her children after years of her own research and because, she said, her nephew had a severe reaction to the vaccine against diphtheria, tetanus and pertussis.” (bold emphasis added)

“ ‘A cough, runny nose, fever and rash to a healthy child is mild but vaccine adverse reactions are severe!!!’ she commented on Jan. 30 on the local hospital’s Facebook post, which described measles symptoms.”

“Brantner’s son Paxton recovered from measles with little problem, she said, after she fed him organic food and cod liver oil, bathed him in magnesium salts and rubbed him in beef tallow cream infused with lavender.”

Fortunately, her son recovered from measles (a good outcome). Both outcome bias (aka, “resulting”) and hindsight bias could affect what she is able to learn from her choices and experiences.⁶ It’s important for us not to be judgmental of people’s choice. As discussed in Part 1, we want to be compassionate and curious. We want to understand how we can support them (and us!) to make better decisions.

Example 2 - Blaming victims

From The Decision Lab: “The hindsight bias may have a role to play in the victim blaming prevalent in sexual assault cases, since people believe survivors should have ‘known better’ in retrospect. Research suggests that hindsight bias contributes to victim derogation in rape cases.”

Example 3 - Political predictions

From The Decision Lab: “A 1993 study asking college students to predict how the U.S. Senate would vote on the confirmation of a Supreme Court nominee supported the influence of the hindsight bias. Before the Senate vote, 58% of students predicted that Thomas would be confirmed. But when students were questioned after the successful confirmation, 78% of them claimed that they originally thought Thomas would be approved.”

Reducing hindsight bias

First, recognize that we all have hindsight bias. Look for the clues: “I should have known.”, etc. Second, for important decisions, fill out a “Knowledge Tracker” (Figure 3). And, third, coach others and your team to recognize hindsight bias and how to protect against it.

Figure 3: Knowledge Tracker (Source: Annie Duke, How to Decide: Simple Tools for Making Better Choices (Penguin Publishing Group, 2020)

From The Decision Lab: “One way to avoid the hindsight bias is to consider and explain how the outcomes that did not unfold could have unfolded. By mentally reviewing all the potential outcomes, an event will seem less inevitable and foreseeable.”

Summary

So far, I have covered two cognitive biases (outcome bias [aka, “resulting”], hindsight bias) because they have a profound impact on making and improving our decisions. If you want a comprehensive and practical introduction to cognitive biases and decision-making, I highly recommend

Olivier Sibony, You’re about to Make a Terrible Mistake!: How Biases Distort Decision-Making--and What You Can Do to Fight Them (New York: Little, Brown Spark, 2020), https://oliviersibony.com/books/.

Thanks for reading this blog. Please share. Feedback welcome.

Serving with you,

Tomás

Resources

I highly recommend Annie Duke’s:

• books,

• Substack blog, or

• live online course (Use PUBLICHEALTH25 to get 25% discount. I do not get any money for informing readers of this discount.)

Footnotes

1. Annie Duke, How to Decide: Simple Tools for Making Better Choices (Penguin Publishing Group, 2020), https://www.annieduke.com/books/.

2. Ibid.

3. “Studies have shown that for children younger than 7 years old, there is a very small increased risk of febrile seizures approximately 6 to 14 days after MMR vaccination; this happens in about 1 in 3,000 to 4,000 children.” (Source: https://www.cdc.gov/vaccine-safety/vaccines/mmr.html)

4. Neal J. Roese and Kathleen D. Vohs, “Hindsight Bias,” Perspectives on Psychological Science: A Journal of the Association for Psychological Science 7, no. 5 (September 2012): 411–26, https://doi.org/10.1177/1745691612454303.

5. Fenit Nirappil and Elana Gordon, “Amid West Texas Measles Outbreak, Vaccine Resistance Hardens -- A Child Has Died in an Outbreak That Has Grown to 146 Cases.,” The Washington Post, March 2, 2025, https://www.washingtonpost.com/health/2025/03/02/measles-outbreak-texas-vaccine-hesitancy-death/.

6. Her prior beliefs and cultural environments (political, religious, informational) are also drivers.