That the mind can wonder is true of absolutely everything. This is not a defense of the baseless criticism that repetition is by nature 'vain'.
Notice how the criticism is walked back to "this could happen", which is a much more mild observation than passing judgment on another's prayer as 'vain' based on its outward appearance without even knowing why it is like that. I dare say that once you know why you are doing what you do, then nothing can ever be seeing as 'vain' again. You can then be seen as lazy if you let your mind wander, but that's why so much of Orthodox practice is focused on being present in mind, body, and spirit during prayer, and having all aspects of existence engaged in the prayer itself, via the prescribed words, physical actions, use of icons, incense, etc.
So I don't even disagree with our friend here, now that the criticism has been softened considerably (and maybe that's how you always meant it, which is fine, but it didn't come out that way at first, so forgive me for not understanding you), but it still misses the mark insofar as this type of criticism is no more valid for Orthodox and Catholic ritual prayer than it would be for literally anything else in the world, because the problem it is assumed to bring about is in actuality a human problem that exists everywhere. If anything, the Orthodox prayer life is the antidote to it, not a manifestation of it. "Father we just wanna" prayers tend to ramble on and on to no good end, as it is actually surprisingly hard to pray without falling into some kind of ritualized/set pattern -- hence I can generalize the type of 'extemporaneous' prayer I am referring to by its usual first line, and I'm going to guess that everyone here will know exactly what I am talking about, since that itself is one form of repetitive prayer by virtue of its having become ritualized/set within an evangelical Protestant/low church context.
So the question is ultimately not "Is this form of prayer good or bad/vain or not", but if you are going to end up following a set pattern anyway because that's how people tend to work (the person who would compose prayer anew every single time he prays is most likely a heretic, as he relies on his own mind rather than what has been left to us), then which is a healthier model -- the ancient ways left to us by the apostles, disciples and other saints who established Christianity in the form of our particular churches, or something that falls out of your brain more or less at random because it feels to you to be more "from the heart" than what others are doing?
I choose the fathers. Others can make whatever choice they'd like to. I'm not the one saying that having another way of praying makes their prayer 'vain', so much as trying to point out the hypocrisy of that (now thankfully diminished) charge coming from anyone who, by virtue of opposing the set prayers on the basis of their repetitiveness alone (rather than theological problems with their content, which would at least be more understandable), shows themselves to have chosen the tradition of themselves instead.
That's nowhere in the Bible. In fact, the Bible states the exact opposite, in 2 Thessalonians 2:15. I don't think our father and master St. Paul the Apostle was advocating any 'vain repetitions' there, or anywhere.
But thanks to Marius for the clarification.
