The planning fallacy is a phenomenon in which predictions about how much time will be needed to complete a future task display an optimism bias and underestimate the time needed.

An Example of the planning fallacy is when someone doesn't allow enough time to complete a project and then is surprised when they don't finish on time.

One way to avoid Planning Fallacy is to use historical data to estimate the time required to complete a task. This can help to provide a more accurate estimate of the time required to complete a task, as opposed to relying on optimistic estimates which often lead to underestimating the time required.