I blogged earlier about an injury I received that has sidelined me. I am not pleased, but the fault is my own. I was practicing without focus.
Focus in the martial arts is particularly important. First, you must practice as you wish to perform. If you wish to be successful in saving your ass in a combat situation, you must absolutely be focused on winning. In order to know what that means, you must be focused in practice. Just like the kata must be felt to be understood, just like ukemei must be felt to be understood, just like torimei must be felt to be understood, focus must be felt to be understood.
Not surprisingly, focus is somewhat hard to describe - it is corollary to being felt to be understood, right? Focus is a matter of clearing your mind so that nothing exists except you and your uke. The samurai called it mushin - no mind. You are acting out of muscle memory.
Aah, but there is more than that. Even before you have the muscle memory, you must concentrate on a lot of other factors in order to learn the technique. That is not trivial. In order to accomplish it, you absolutely must not be thinking about being hungry, or your job, or your homework, or your wife, or your sore leg, or your gi, or the cute chick that joined class today, or the fact that your buddy missed class. Just the technique. Nothing else.
That in itself takes practice - which makes it even more of an important part of practice. (I mentioned that this is complicated.) I wasn't focused on my own ukemei, so I let me legs flop around, and one of them ended up under my tori's knee - which was exactly where it was supposed to be. Uke have responsibility for focus too.
So lesson learned. If you aren't able to focus, don't go to class. Or meditate before class and get that focus back. But don't ever, EVER practice without focus.