I have prayed that prayer before. Many times, actually. From my experience (I can't speak for MissCriss, though it may be similar, I don't know), my flesh and my will are weak. I will resolve to be more disciplined, to be more vulnerable with God, and then a week later, I'm back to my old habits.
For me, I have evaluate myself every day, pretty much. Sometimes I'm lazy and I don't. Sometimes I'm "busy" (which is not an excuse). Sometimes I just...don't.
Maybe someday my flesh will not win so often. Maybe I'm going about it the wrong way. Becuase you're right, the truth does set us free. I believe we are already free in that. Our chains are gone. But sometimes we still hold onto things of the world and feel tied down when we shouldn't.
It's like this picture.
The horse is obviously stronger than the chair and could just drag that chair around. But he doesn't. He thinks he is powerless. Sometimes I feel like that. I know Christ is stronger than that chair (my sin, my spiritual laziness, etc.) but sometimes I must work through struggles and issues in my mind, get out of that muck and mire, before I can realize that Christ is Almighty over my problems. The best part is that He's there with me even through the muck and the mire. Sometimes I ignore Him in it (not good) but what I should do is cling to Him throughout it instead of trying to work on it on my own.
Now I feel like I'm rambling without making sense. In my mind I was going somewhere with this, but now I feel not so much.
TLDR; God sets us free, it's true. But, we still war against our wordly flesh/mind, and that can be quite a battle sometimes.