I attended an excellent class on Scrum a couple of weeks ago. I've always been a bit of a skeptic of formal project management or development frameworks, but I have to say that I was impressed. Some elements of scrum are really either common sense, such as the need for transparency, and others, such as short development cycles that result in an always functioning system hold real promise.
The one aspect of scrum that I identified most with, however, was "discover and adapt." In order to be successful in testing software, you always have to operating in a discover and adapt mode. You can define a detailed test plan, and base that plan on the best information available at the time, but in the course of a software project test cycle, you have to constantly re-evaluate the current state of the software under test, and then adapt your future plans to match. You may start off by testing subsystem A, but then find that its testing is blocked, but you can continue to make progress by testing subsystem B.
One crucial part of your adapting to what you discover about the software under test, is that your priorities for testing will always change. You highest priority will always be to run tests that will find the most serious as yet undiscovered bug. But, the places in the code where that bug may be lurking can change as either the code changes, or your understanding of the code increases.
There's a great analogy for "discover and adapt" in sports. (And, no, it doesn't involve golf this time. ;-) It involves American baseball, and concerns the sometimes under appreciated skill of base running.
When you think about what it takes to be a great base runner, you might think that the only factor is speed. Speed is important, to be sure, but what is even more important is the base runner's judgment. He has to be able to adapt quickly to changing situations, and decide when to be aggressive and "take the extra base," and when to be more conservative. In short, he has to discover and adapt. How does he do this? He watches the ball and the opposing players, not the bases. The bases aren't changing, the position of the ball and those players is.
I found this wonderful passage about Joe DiMaggio in David Halberstam's book "Summer of '49" that describes this:
...Stengel, his new manager, was equally impressed, and when DiMaggio was on base he would point to him as an example of the perfect base runner. "Look at him," Stengel would say as DiMaggio ran out a base hit, "he's always watching the ball. He isn't watching second base. He isn't watching third base. He knows they haven't been moved. He isn't watching the ground, because he knows they haven't built a canal or a swimming pool since he was last there. He's watching the ball and the outfielder, which is the one thing that is different on every play..."
It's like that in software too. You can't keep your eye on static plans, you have to keep your eye on the current (and changing) state of the project and the code, and always discover and adapt.
 Halberstam, David, "Summer of '49,", (Morrow: New York), 1989. http://www.amazon.com/Summer-49-P-S-David-Halberstam/dp/0060884266/ref=sr_1_1?ie=UTF8&s=books&qid=1255145843&sr=8-1