A manager assigned a project to a developer. When the developer had sufficient time to review the project, the manager asked "How long will it take to complete?"
"A lifetime," replied the developer.
"Be serious," the manager scolded, "we need this much sooner than that. How long will it take to satisfy the customer's needs?"
The developer asked: "What are their needs?"
After discussing the user needs at length the developer said, "Doing this will take me three days."
The manager, still not satisfied, said, "That is not fast enough! What if you work as quickly as possible? How long then?"
After careful consideration, the developer answered, "Four days."