Kokoro which means heart in english. It is your will to survive even when the odds are against you. It is also partly your dedication to your training or your job or whatever way it is that you follow. I think that kokoro is more like your spirit or your soul, one that has a strong spirit has much kokoro. One with much kokoro can endure through many hardships in his or her life. Something that I believe kokoro is not, is how hard you fight for things you believe in. What I mean by this is not that you shouldn't fight for what you believe in, but do not fight for it just to persuade others to believe the same thing. An example is if someone is trying to force you to do something that is against your beliefs then I think you should fight for them. However if someone says your beliefs are stupid that doesn't mean you should beat them up or even become angered by it, they are just as entitled to their beliefs as you are to yours. And the only one you need to prove your beliefs to is yourself. I am not saying that it is wrong to discuss your beliefs, but I don't think you should argue about them just to prove you are right or just to argue.