Why it was said

Jason Fried and David Heinemeier Hansson give a chapter this title in the opening section of Rework. It is the shortest argument in a book of short arguments: long-term plans are written before the information exists.

What it actually means

A plan written before there is a customer is fiction with a spreadsheet. The authors are not against thinking ahead; they are against pretending that a document written in January knows what June will bring, and against the way such documents get defended once written. Calling it guessing restores the right relationship: guess, act, look, and guess again with what you learned.

How to use it

1. 1Write the plan on one page and rewrite it whenever a customer teaches you something.
2. 2When a plan is being defended, ask what was known when it was written.