Suppose you had the following conversation with your friend:
Today I'm only going to speak German.
Do you even know how to speak German?
I bought a book to help -- Darn it!... Er, Ich... kaufte ein Buch... helfen.... Oh, this will never work. I can't speak German. I'll never be able to speak German!
I think it would be reasonable to conclude that your friend was expecting too much of himself right away, and therefore expecting too little of himself over time.
And I think most people would understand this, that a person can't just switch from the language he's spoken all his life to a language he hasn't spoken much, if at all.
So why do some people say, in effect, "Today I'm going to pray like a saint," then get frustrated when they fail to pray like a saint?
Prayer is no less a habit than speaking a particular langauge. Just as speaking a new language in place of an old language requires both developing a new habit and breaking an old habit, so too does prayer require, not just developing the habit of prayer, but also breaking the old habit of, in Romano Guardini's words as quoted on Flos Carmeli, being "incapable of standing still or of concentrating."
Steven Riddle goes on to consider the problem of recollectedness. To his post I would only add that most of us should neither assume recollectedness will require no effort to attain nor conclude that we will never attain it.