Fairly obvious, but if you do dumb things and expect a general methodology to save you, it won't. Or, like it is said in fitness world, "you cannot out-train a bad diet".

Moreover, if you have people in your team that are not aligned with the methodology ("I'd rather be doing X", "It slows me down as a developer" etc.) the results will be sub-par. Applying a methodology requires a certain level of mindfulness which doesn't seem to be common these days.