It works like magic
I was confused by unbendable arm for some time. I just didn't understand the concept. I read "Aikido and the Dynamic Sphere" and tried the visualization it described, and it worked! Only after I had experienced it did I think about the scientific explanation and start to "understand" it that way as well.
So, for me, ki works _like_ magic, but I don't believe it _is_ magic. The important thing is that visualizing ki works. Somehow the concept works with the body to achieve the results.
So I stopped worrying about the mechanics and science, and started using ki. I still analyse things sometimes, but it's just out of curiousity, and not necessary for my practice.
I think this was one of the most important steps in my training so far.