A project looks simple when you picture it in advance.
Write the report.
Paint the room.
Drive to the airport.
Build the shelf.
Then reality arrives.
The printer stops working.
The paint needs another coat.
Traffic backs up.
One missing screw sends you to the hardware store.
Psychologists call this the planning fallacy.
We picture the main steps
When imagining a future task, people tend to focus on the ideal sequence.
Step one.
Step two.
Step three.
That mental simulation usually leaves out random delays.
Reality includes interruptions
Real projects contain extra work.
Emails.
Mistakes.
Missing information.
Waiting for other people.
Finding tools.
Fixing things that were supposed to work.
The plan includes the task.
Reality includes the task plus reality.
Why do past delays not fix our estimates?
We often treat previous problems as special cases.
“Last time was unusual.”
“The printer broke.”
“Traffic was terrible.”
“This time will be different.”
Sometimes it is.
Often the same general category of unexpected problem simply arrives wearing a new outfit.
What is a better way to estimate?
Use the outside view.
Instead of asking only, “How long should this take?” ask, “How long did similar tasks actually take in the past?”
Historical averages include real-world delays automatically.
Why are we optimistic about our future selves?
Future versions of ourselves are extremely efficient.
They never get tired.
They never get interrupted.
They immediately find the charger.
Actual future us is still a human being.
That gap helps produce unrealistic plans.
Is optimism always bad?
No.
Optimism helps people start difficult projects.
The problem is when scheduling depends on best-case assumptions.
A little margin for ordinary problems is not pessimism.
It is realism.
Apparently every future version of ourselves is faster, better organized, and completely immune to interruptions.
A related piece of human behavior appears in Why do unfinished tasks stay in your mind?, where the brain handles another everyday judgment or response.
And that’s the short explanation.
Related explanations: Why do unfinished tasks stay in your mind?, Why do we procrastinate?, and Why can having more choices make choosing harder?