...there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns -- the ones we don't know we don't know.

- Donald Rumsfeld US Secretary of Defense

Too many developers hated planning because the plan had never been of any personal benefit to them. Instead, plans were often used as weapons used against the developers

- Succeeding with Agile, Mike Cohn