The Planning fallacy is the tendency to underestimate the time needed to complete tasks. The planning fallacy actually stems from another error, The Optimism Bias, which is the tendency for individuals to be overly positive about the outcome of planned actions. People are more susceptible to the planning fallacy when the task is something they have never done before. The reason for this is because we estimate based on past experiences. For example, if I asked you how long it takes you to grocery shop, you will consider how long it has taken you in the past, and you will have a reasonable answer. If I ask you how long it will take you to do something you have never done before, like completing a thesis or climbing Mount Everest, you have no experience to reference, and because of your inherent optimism, you will guesstimate less time than you really need. To help you with this fallacy, remember Hofstadter’s Law: It always takes longer than you expect, even when you take into account Hofstadter’s Law.
Interesting Fact: “Realistic pessimism” is a phenomenon where depressed or overly pessimistic people more accurately predict task completion estimations.
Source: Listverse again!