From the replies, it seems people are missing the point here, which is not that decisive battles do not exist (they do), but rather that they never result in eternal victory. It's a similar category to "this will be a quick war".
Yet another example of "the politics sickos need to read more military theory" is the fact that so many politics sickos seem to be wedded to the idea that a decisive battle is the One Simple Trick that will result in eternal victory