> Whether a methodology works or not depends on the criteria: team productivity, happiness, retention, conformity, predictability, accountability, communication, lines per day, man-months, code quality, artifacts produced, etc. Every methodology works if you measure the right thing. But in terms of the only measurement that really matters—satisfying requirements on time and within budget—I haven’t seen any methodology deliver consistent results.
Asking a methodology to always meet requirements on time and within budget is asking for human perfection. You might as well expect it to deliver world peace and end hunger as we know it as well. So of course if you set a ludicrously unattainable goal, development methodologies all fail. In every project, unforeseen obstacles will always come up, which usually means some combination of scope-cutting or delaying or (occasionally) spending more.
But when teams are having major problems in delivering working code at all or at a reasonable pace, that's where different methodologies can absolutely improve the situation, depending on what's going wrong and what the desired product is. So obviously they do work in terms of adding value, when applied appropriately.
Let's not throw the baby out with the bathwater here.