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planning fallacy

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The demonstrated tendency for people to underestimate the length of time it will take them to complete a task. Various explanations have been offered, including optimism bias, failure to allow for extraneous factors such as sickness etc., and the wish to make a good impression when submitting plans for approval. One counterintuitive finding of studies in this area is that the more detailed and specific the plan, the more likely it is to be seriously overoptimistic. This is perhaps because detailed planning (i) encourages people to suppose that everything will go according to plan; and (ii) narrows their focus so they fail to consider factors outside the plan (e.g. defaults by suppliers, accidents, unexpected events of all kinds). The best antidote to planning fallacy is to research how long comparable projects have taken in the past (which can be accurately known), rather than making assumptions about the future (which cannot). See also Hofstadter's law; strategic misrepresentation.

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