When knowing something is disadvantageous: the curse of knowledge

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Reasoning on what others are thinking is a fundamental activity for a human being, if he wants to interpret the behavior of others. Knowing how to put yourself in someone’s shoes is essential, in any other way it is impossible to be able to predict the decision of others.

This is particularly difficult for children, especially for those that are younger than 4 years old. Most of the research aimed at analyzing the reasoning of children on false beliefs of others has used some type of variant of the displacement task.

In this type of experiment, the children are told the story of a person, for example named Andrea, that puts her candy inside a box, then leaving the room. At this point, another character, Barbara, moves the candy in a basket, while Andrea is absent. Then the children are asked to indicate the container in which Andrea, now back in the room, will look for the candy.

The correct answer, that she will look inside the box, implies the attribution of a false belief to Andrea. Children younger than 4 years old obtain good performances in this test, but younger children tend to answer in the wrong way. Their knowledge influences the reasoning on false beliefs.

If this can seem only a limitation due to the young age, this same cognitive error, then classified as the bias of the curse of knowledge, can be found even in adults, if the test is presented in a more refined way.

A new test

Susan Birch and Paul Bloom, the former from the University of Vancouver and the latter from Yale, wanted thus to test if this effect was present even in adults, in other words if the reasoning on false beliefs was more difficult if they know about the final outcome. The test they proposed to the participants differed in three main ways from the traditional displacement task, too simple if presented to adults:

    1. The different probabilities for each container that the protagonist could look in were asked to the subjects, instead of the single container,
    1. Four containers were used, instead of two,
    1. To investigate the plausibility of the protagonist’s choice, the position of the containers was changed.

It had actually been proved by previous research that the plausibility was correlated to the entity of the effect of the curse of knowledge. In other words, the more plausible a factor can lead the protagonist to the wrong choice, the more one is influenced by this cognitive error.

Reasoning on what others are thinking is a fundamental activity for a human being, if he wants to interpret the behaviors of others.

A violin

To test this last point, 155 participants underwent the experiment under three different conditions: ignorance, knowledge-plausible, knowledge-implausible. The experiment started with a text: “This is Vicki. She finishes playing her violin and puts it in the blue container. Then she goes outside to play. While Vicki is outside playing, her sister, Denise…”. At this point, depending on the condition, the text differed:

    • Ignorance: “moves the violin to another container.”,
    • Knowledge-plausible: “moves the violin to the red container.”,
    • Knowledge-implausible: “moves the violin to the purple container.”.

The indications were then the same for all participants: “Then, Denise rearranges the containers in the room until the room looks like the picture below.”. Before, from the left to the right, the containers were blue, purple, red and green. After Denise changed the positions, they were red, green, purple and blue.

To conclude: “When Vicki returns, she wants to play her violin. What are the chances Vicki will first look for her violin in each of the above containers? Write your answers in percentages in the spaces provided under each container.”.

The results

In the ignorance condition, the subjects gave an average chance of 71% to the blue container, therefore the same in which Vicky had put the violin initially, and 23% to the red one, the container that occupied the position of the blue one after Denise exchanged them. Therefore, the subjects considered plausible, and not probable, that Vicki would look in a different container than that in which she had put the violin, as it occupied the same position.

In the knowledge-plausible condition, in which the subjects knew that Denise had moved the violin in the red container, they assigned a much higher chance to this container than the ignorance group, balanced by a lower chance for the blue one. Their knowledge of the outcome had influenced their prediction on Vicki.

Conversely, the implausible-knowledge condition assigned on average a low chance for the purple container, as there wasn’t a plausible reason for Vicki to look in a container in which she had neither put the violin, nor it occupied the position of the same container. The assigned chance for the purple container was not significantly higher than that of the ignorance group.

The results seemed to confirm the fact the knowledge is a curse only if there is a plausible explanation for the protagonist to take a decision that differs from the most probable one.

Not only the children, then, are victim of this bias. A reason that would explain the cause of this effect in children, the researchers suggest, is that the kids, especially younger than 4 years old, don’t yet possess or fully comprehend the concept of plausibility and probability. Growing up, one becomes more resistant, but never immune to this type of bias.

Carlo Sordini


  1. Birch, S. A., & Bloom, P. (2007). The curse of knowledge in reasoning about false beliefs. Psychological science, 18(5), 382–386. https://doi.org/10.1111/j.1467-9280.2007.01909.x
  2. Birch, S. (2005). When Knowledge Is a Curse: Children’s and Adults’ Reasoning about Mental States. Current Directions in Psychological Science, 14(1), 25-29. Retrieved July 26, 2021, from http://www.jstor.org/stable/20182979

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