That’s not to say we should stop planning. We still need to plan—and understand variations from the plans—but plans are not to be set in stone; they are meant to be flexible.
Agile emphasizes empirical process control. This is the idea behind inspect and adapt. Many Agile practices are all about this intent, such as: Scrum’s sprint retrospectives, Lean’s kaizen, and XP’s weekly iterations and short releases. These practices are about looking back and adapting: constantly recalibrating, improving, and doing course control.