Oddly Wired
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planning

You consistently underestimate how much time a task requires.

People exhibit a deep-seated bias to overlook potential obstacles when creating their own personal schedules.

Even when you have failed to finish similar tasks on time in the past, you remain optimistic that the current project will proceed without interruption. You plan for the best-case scenario and ignore the inevitable friction of everyday life.

Your schedule is a wishlist, not a realistic prediction.

Where this comes from

Study
Buehler, Griffin, and Ross (1994)
What the check found
The planning fallacy is a well-established psychological phenomenon. While the provided reference material was irrelevant and contained no supporting text, the attribution to the 1994 study is accurate.
Confidence
Solid, with limits

Related

One of these every day, and every one names the study it came from. When a finding is contested, it says so.