A traditional project plan has an ethos, “Plan the work, work the plan.” The planning process will work out all the expected tasks, estimate them all, and assign workers to the tasks. This has several problems: the sheer mass of data makes it hard to see what’s really important, the plan is vulnerable to changes in direction, and it’s hard to keep up to date.
XP and Scrum (and some but not all other agile methods) take a different approach: the set of features currently under development is tracked at a high level of detail (with an iteration plan or sprint backlog), the set of features planned for the next release are tracked at less detail (release plan or product backlog), and features further out are tracked at even less detail.
There’s a type of lens known as a fisheye lens. (You can see a sample picture taken by a fisheye lens). This lens gets a 180-degree field of view, so it shows a much wider area than a typical lens. But it does it in a way that appears distorted: things in the center appear mostly normal, but as you get closer to the edge, it looks more distorted.
I see the agile methods described above as acting like that: lots of detail in the center (the now), and less detail in the periphery (the future), but still enough detail to let you make sense of the big picture. When you consider that agile methods focus on high business value first (slicing by feature rather than by technology), they truly focus on what’s important.
(For more on XP, see xp123.com, www.xprogramming.com, or www.extremeprogramming.org; for information on Scrum, see www.controlchaos.com.)