What Plans Are

Planning is the way we steer an XP project. We use stories to sketch out where
we would like to go. We defer specifying details for stories until the iteration in
which we'll code them. We make small adjustments as we go.
Planning minimizes your chances of ending up in a ditch, and can help you get
out one when you're in it. Plan like people were said to have voted in Chicago in
1968: early and often.
If you don't have a map you'll get lost. If you never deviate from the map,
you'll probably miss lots of good stuff that is off the beaten path. Thus, we come up
with a plan but we're willing to stray from it.
Paul Grobstein said that the concept of being "right" should be replaced with
that of being "progressively less wrong." The former measures your success or
failure by proximity to a fixed point, a target, set at the beginning. This encourages
people to put on blinders. The latter measures your success or failure by charting
your progress from your starting point. This encourages exploration, respect for experience, and the appreciation of the value of each individual's perspective on a
problem. XP planning is all about learning, and then applying the lessons learned as
soon as possible. We hope to be "progressively less wrong" over time.