Even if you’ve never heard of the planning fallacy, you’ve probably experienced it. It’s a phenomenon where a person or team underestimates how long a task will take and how much it will cost in money or resources, and overestimates the actual benefits it will bring. If you’ve ever waited until the last minute to respond to an email, only to realize that you don’t have the data you need to send a proper response, you’ve fallen victim to the planning fallacy. In fact, you’ve fallen victim if you’ve ever been late for something because you were just sure that traffic wouldn’t stop you from getting there, even though there was always traffic along that route at that time — but there are ways to get around it.

As mentioned, the planning fallacy is simply a pattern of faulty thinking that causes people to mismanage their time or expectations. You don’t realize how much time a task will actually take, how much you have to spend on it, or how little you’ll get out of it. The fallacy itself was first introduced by economist Daniel Kahneman and cognitive psychologist Amos Tversky in 1979, but was expanded in 2003 to include the overestimation of favorable outcomes.

Over the years it has been researched and proven by other great thinkers who have come to the conclusion that it is all part of an optimistic bias that causes people to look at the future through rose-colored glasses instead of thinking realistically about their plans and expected outcomes.

That is to say, generally speaking, when you plan your day or your projects, you are probably strategizing around the best case scenario: investing little time and resources with a high return, rather than the worst case scenario. This means that if (perhaps when) things don’t go well, you are not prepared.